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2524d4cb55
The existing deadlock detector code uses the trace-malloc stack walking facilities, which is problematic for a few reasons. 1. It is only available in builds with --enable-trace-malloc, which is not in the default build configuration. 2. It tries to capture a symbolicated stack trace every time that a lock is acquired or released, which is really slow. This patch changes the deadlock detector to use the XPCOM stack walking and symbolification facilities, and avoids the symbolification until the point where we need to print out the call stack, which makes the deadlock detector a lot faster than it currently is in trace-malloc builds.
542 lines
18 KiB
C++
542 lines
18 KiB
C++
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: sw=4 ts=4 et :
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_DeadlockDetector_h
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#define mozilla_DeadlockDetector_h
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#include "mozilla/Attributes.h"
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#include "mozilla/Move.h"
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#include <stdlib.h>
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#include "plhash.h"
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#include "prlock.h"
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#include "nsTArray.h"
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namespace mozilla {
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class NS_COM_GLUE CallStack
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{
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private:
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nsTArray<void*> mCallStack;
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public:
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/**
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* CallStack
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* *ALWAYS* *ALWAYS* *ALWAYS* call this with no arguments. This
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* constructor takes an argument *ONLY* so that |GET_BACKTRACE()|
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* can be evaluated in the stack frame of the caller, rather than
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* that of the constructor.
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*
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* *BEWARE*: this means that calling this constructor with no
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* arguments is not the same as a "default, do-nothing"
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* constructor: it *will* construct a backtrace. This can cause
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* unexpected performance issues.
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*/
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CallStack(const nsTArray<void*>& aCallStack = GetBacktrace()) :
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mCallStack(mozilla::Move(aCallStack))
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{
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}
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CallStack(const CallStack& aFrom) :
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mCallStack(aFrom.mCallStack)
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{
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}
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CallStack& operator=(const CallStack& aFrom)
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{
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mCallStack = aFrom.mCallStack;
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return *this;
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}
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bool operator==(const CallStack& aOther) const
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{
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return mCallStack == aOther.mCallStack;
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}
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bool operator!=(const CallStack& aOther) const
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{
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return mCallStack != aOther.mCallStack;
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}
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bool IsEmpty() const
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{
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return mCallStack.IsEmpty();
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}
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void Print(FILE* f) const;
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static nsTArray<void*> GetBacktrace();
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static const CallStack NullCallStack()
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{
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return CallStack(nsTArray<void*>());
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}
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};
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/**
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* DeadlockDetector
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*
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* The following is an approximate description of how the deadlock detector
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* works.
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*
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* The deadlock detector ensures that all blocking resources are
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* acquired according to a partial order P. One type of blocking
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* resource is a lock. If a lock l1 is acquired (locked) before l2,
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* then we say that |l1 <_P l2|. The detector flags an error if two
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* locks l1 and l2 have an inconsistent ordering in P; that is, if
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* both |l1 <_P l2| and |l2 <_P l1|. This is a potential error
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* because a thread acquiring l1,l2 according to the first order might
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* race with a thread acquiring them according to the second order.
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* If this happens under the right conditions, then the acquisitions
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* will deadlock.
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*
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* This deadlock detector doesn't know at compile-time what P is. So,
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* it tries to discover the order at run time. More precisely, it
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* finds <i>some</i> order P, then tries to find chains of resource
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* acquisitions that violate P. An example acquisition sequence, and
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* the orders they impose, is
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* l1.lock() // current chain: [ l1 ]
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* // order: { }
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*
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* l2.lock() // current chain: [ l1, l2 ]
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* // order: { l1 <_P l2 }
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*
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* l3.lock() // current chain: [ l1, l2, l3 ]
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* // order: { l1 <_P l2, l2 <_P l3, l1 <_P l3 }
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* // (note: <_P is transitive, so also |l1 <_P l3|)
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*
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* l2.unlock() // current chain: [ l1, l3 ]
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* // order: { l1 <_P l2, l2 <_P l3, l1 <_P l3 }
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* // (note: it's OK, but weird, that l2 was unlocked out
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* // of order. we still have l1 <_P l3).
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*
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* l2.lock() // current chain: [ l1, l3, l2 ]
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* // order: { l1 <_P l2, l2 <_P l3, l1 <_P l3,
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* l3 <_P l2 (!!!) }
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* BEEP BEEP! Here the detector will flag a potential error, since
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* l2 and l3 were used inconsistently (and potentially in ways that
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* would deadlock).
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*/
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template <typename T>
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class DeadlockDetector
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{
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public:
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/**
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* ResourceAcquisition
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* Consists simply of a resource and the calling context from
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* which it was acquired. We pack this information together so
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* that it can be returned back to the caller when a potential
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* deadlock has been found.
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*/
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struct ResourceAcquisition
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{
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const T* mResource;
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CallStack mCallContext;
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ResourceAcquisition(
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const T* aResource,
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const CallStack aCallContext=CallStack::NullCallStack()) :
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mResource(aResource),
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mCallContext(aCallContext)
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{
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}
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ResourceAcquisition(const ResourceAcquisition& aFrom) :
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mResource(aFrom.mResource),
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mCallContext(aFrom.mCallContext)
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{
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}
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ResourceAcquisition& operator=(const ResourceAcquisition& aFrom)
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{
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mResource = aFrom.mResource;
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mCallContext = aFrom.mCallContext;
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return *this;
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}
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};
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typedef nsTArray<ResourceAcquisition> ResourceAcquisitionArray;
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private:
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typedef nsTArray<PLHashEntry*> HashEntryArray;
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typedef typename HashEntryArray::index_type index_type;
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typedef typename HashEntryArray::size_type size_type;
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enum {
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NoIndex = HashEntryArray::NoIndex
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};
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/**
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* Value type for the ordering table. Contains the other
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* resources on which an ordering constraint |key < other|
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* exists. The catch is that we also store the calling context at
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* which the other resource was acquired; this improves the
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* quality of error messages when potential deadlock is detected.
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*/
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struct OrderingEntry
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{
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OrderingEntry() :
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mFirstSeen(CallStack::NullCallStack()),
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mOrderedLT() // FIXME bug 456272: set to empirical
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{ // dep size?
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}
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~OrderingEntry()
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{
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}
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CallStack mFirstSeen; // first site from which the resource appeared
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HashEntryArray mOrderedLT; // this <_o Other
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};
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static void* TableAlloc(void* /*pool*/, size_t size)
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{
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return operator new(size);
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}
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static void TableFree(void* /*pool*/, void* item)
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{
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operator delete(item);
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}
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static PLHashEntry* EntryAlloc(void* /*pool*/, const void* key)
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{
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return new PLHashEntry;
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}
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static void EntryFree(void* /*pool*/, PLHashEntry* entry, unsigned flag)
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{
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delete static_cast<T*>(const_cast<void*>(entry->key));
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delete static_cast<OrderingEntry*>(entry->value);
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entry->value = 0;
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if (HT_FREE_ENTRY == flag)
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delete entry;
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}
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static PLHashNumber HashKey(const void* aKey)
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{
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return NS_PTR_TO_INT32(aKey) >> 2;
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}
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static const PLHashAllocOps kAllocOps;
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// Hash table "interface" the rest of the code should use
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PLHashEntry** GetEntry(const T* aKey)
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{
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return PL_HashTableRawLookup(mOrdering, HashKey(aKey), aKey);
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}
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void PutEntry(T* aKey)
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{
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PL_HashTableAdd(mOrdering, aKey, new OrderingEntry());
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}
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// XXX need these helper methods because OrderingEntry doesn't have
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// XXX access to underlying PLHashEntry
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/**
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* Add the order |aFirst <_o aSecond|.
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*
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* WARNING: this does not check whether it's sane to add this
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* order. In the "best" bad case, when this order already exists,
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* adding it anyway may unnecessarily result in O(n^2) space. In
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* the "worst" bad case, adding it anyway will cause
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* |InTransitiveClosure()| to diverge.
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*/
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void AddOrder(PLHashEntry* aLT, PLHashEntry* aGT)
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{
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static_cast<OrderingEntry*>(aLT->value)->mOrderedLT
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.InsertElementSorted(aGT);
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}
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/**
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* Return true iff the order |aFirst < aSecond| has been
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* *explicitly* added.
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*
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* Does not consider transitivity.
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*/
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bool IsOrdered(const PLHashEntry* aFirst, const PLHashEntry* aSecond)
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const
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{
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return NoIndex !=
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static_cast<const OrderingEntry*>(aFirst->value)->mOrderedLT
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.BinaryIndexOf(aSecond);
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}
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/**
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* Return a pointer to the array of all elements "that" for
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* which the order |this < that| has been explicitly added.
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*
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* NOTE: this does *not* consider transitive orderings.
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*/
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PLHashEntry* const* GetOrders(const PLHashEntry* aEntry) const
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{
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return static_cast<const OrderingEntry*>(aEntry->value)->mOrderedLT
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.Elements();
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}
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/**
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* Return the number of elements "that" for which the order
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* |this < that| has been explicitly added.
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*
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* NOTE: this does *not* consider transitive orderings.
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*/
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size_type NumOrders(const PLHashEntry* aEntry) const
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{
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return static_cast<const OrderingEntry*>(aEntry->value)->mOrderedLT
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.Length();
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}
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/** Make a ResourceAcquisition out of |aEntry|. */
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ResourceAcquisition MakeResourceAcquisition(const PLHashEntry* aEntry)
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const
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{
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return ResourceAcquisition(
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static_cast<const T*>(aEntry->key),
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static_cast<const OrderingEntry*>(aEntry->value)->mFirstSeen);
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}
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// Throwaway RAII lock to make the following code safer.
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struct PRAutoLock
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{
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PRAutoLock(PRLock* aLock) : mLock(aLock) { PR_Lock(mLock); }
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~PRAutoLock() { PR_Unlock(mLock); }
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PRLock* mLock;
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};
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public:
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static const uint32_t kDefaultNumBuckets;
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/**
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* DeadlockDetector
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* Create a new deadlock detector.
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*
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* @param aNumResourcesGuess Guess at approximate number of resources
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* that will be checked.
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*/
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DeadlockDetector(uint32_t aNumResourcesGuess = kDefaultNumBuckets)
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{
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mOrdering = PL_NewHashTable(aNumResourcesGuess,
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HashKey,
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PL_CompareValues, PL_CompareValues,
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&kAllocOps, 0);
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if (!mOrdering)
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NS_RUNTIMEABORT("couldn't initialize resource ordering table");
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mLock = PR_NewLock();
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if (!mLock)
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NS_RUNTIMEABORT("couldn't allocate deadlock detector lock");
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}
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/**
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* ~DeadlockDetector
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*
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* *NOT* thread safe.
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*/
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~DeadlockDetector()
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{
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PL_HashTableDestroy(mOrdering);
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PR_DestroyLock(mLock);
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}
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/**
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* Add
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* Make the deadlock detector aware of |aResource|.
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*
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* WARNING: The deadlock detector owns |aResource|.
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*
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* Thread safe.
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*
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* @param aResource Resource to make deadlock detector aware of.
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*/
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void Add(T* aResource)
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{
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PRAutoLock _(mLock);
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PutEntry(aResource);
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}
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// Nb: implementing a Remove() method makes the detector "more
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// unsound." By removing a resource from the orderings, deadlocks
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// may be missed that would otherwise have been found. However,
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// removing resources possibly reduces the # of false positives,
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// and additionally saves space. So it's a trade off; we have
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// chosen to err on the side of caution and not implement Remove().
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/**
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* CheckAcquisition This method is called after acquiring |aLast|,
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* but before trying to acquire |aProposed| from |aCallContext|.
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* It determines whether actually trying to acquire |aProposed|
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* will create problems. It is OK if |aLast| is nullptr; this is
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* interpreted as |aProposed| being the thread's first acquisition
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* of its current chain.
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*
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* Iff acquiring |aProposed| may lead to deadlock for some thread
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* interleaving (including the current one!), the cyclical
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* dependency from which this was deduced is returned. Otherwise,
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* 0 is returned.
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*
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* If a potential deadlock is detected and a resource cycle is
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* returned, it is the *caller's* responsibility to free it.
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*
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* Thread safe.
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*
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* @param aLast Last resource acquired by calling thread (or 0).
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* @param aProposed Resource calling thread proposes to acquire.
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* @param aCallContext Calling context whence acquisiton request came.
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*/
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ResourceAcquisitionArray* CheckAcquisition(const T* aLast,
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const T* aProposed,
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const CallStack& aCallContext)
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{
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NS_ASSERTION(aProposed, "null resource");
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PRAutoLock _(mLock);
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PLHashEntry* second = *GetEntry(aProposed);
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OrderingEntry* e = static_cast<OrderingEntry*>(second->value);
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if (e->mFirstSeen.IsEmpty())
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e->mFirstSeen = aCallContext;
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if (!aLast)
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// don't check if |0 < proposed|; just vamoose
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return 0;
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PLHashEntry* first = *GetEntry(aLast);
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// this is the crux of the deadlock detector algorithm
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if (first == second) {
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// reflexive deadlock. fastpath b/c InTransitiveClosure is
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// not applicable here.
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ResourceAcquisitionArray* cycle = new ResourceAcquisitionArray();
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if (!cycle)
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NS_RUNTIMEABORT("can't allocate dep. cycle array");
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cycle->AppendElement(MakeResourceAcquisition(first));
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cycle->AppendElement(ResourceAcquisition(aProposed,
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aCallContext));
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return cycle;
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}
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if (InTransitiveClosure(first, second)) {
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// we've already established |last < proposed|. all is well.
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return 0;
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}
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if (InTransitiveClosure(second, first)) {
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// the order |proposed < last| has been deduced, perhaps
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// transitively. we're attempting to violate that
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// constraint by acquiring resources in the order
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// |last < proposed|, and thus we may deadlock under the
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// right conditions.
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ResourceAcquisitionArray* cycle = GetDeductionChain(second, first);
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// show how acquiring |proposed| would complete the cycle
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cycle->AppendElement(ResourceAcquisition(aProposed,
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aCallContext));
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return cycle;
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}
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// |last|, |proposed| are unordered according to our
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// poset. this is fine, but we now need to add this
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// ordering constraint.
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AddOrder(first, second);
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return 0;
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}
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/**
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* Return true iff |aTarget| is in the transitive closure of |aStart|
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* over the ordering relation `<_this'.
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*
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* @precondition |aStart != aTarget|
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*/
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bool InTransitiveClosure(const PLHashEntry* aStart,
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const PLHashEntry* aTarget) const
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{
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if (IsOrdered(aStart, aTarget))
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return true;
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index_type i = 0;
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size_type len = NumOrders(aStart);
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for (const PLHashEntry* const* it = GetOrders(aStart);
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i < len; ++i, ++it)
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if (InTransitiveClosure(*it, aTarget))
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return true;
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return false;
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}
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/**
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* Return an array of all resource acquisitions
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* aStart <_this r1 <_this r2 <_ ... <_ aTarget
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* from which |aStart <_this aTarget| was deduced, including
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* |aStart| and |aTarget|.
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*
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* Nb: there may be multiple deductions of |aStart <_this
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* aTarget|. This function returns the first ordering found by
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* depth-first search.
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*
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* Nb: |InTransitiveClosure| could be replaced by this function.
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* However, this one is more expensive because we record the DFS
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* search stack on the heap whereas the other doesn't.
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*
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* @precondition |aStart != aTarget|
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*/
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ResourceAcquisitionArray* GetDeductionChain(
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const PLHashEntry* aStart,
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const PLHashEntry* aTarget)
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{
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ResourceAcquisitionArray* chain = new ResourceAcquisitionArray();
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if (!chain)
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NS_RUNTIMEABORT("can't allocate dep. cycle array");
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chain->AppendElement(MakeResourceAcquisition(aStart));
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NS_ASSERTION(GetDeductionChain_Helper(aStart, aTarget, chain),
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"GetDeductionChain called when there's no deadlock");
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return chain;
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}
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// precondition: |aStart != aTarget|
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// invariant: |aStart| is the last element in |aChain|
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bool GetDeductionChain_Helper(const PLHashEntry* aStart,
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const PLHashEntry* aTarget,
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ResourceAcquisitionArray* aChain)
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{
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if (IsOrdered(aStart, aTarget)) {
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aChain->AppendElement(MakeResourceAcquisition(aTarget));
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return true;
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}
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index_type i = 0;
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size_type len = NumOrders(aStart);
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for (const PLHashEntry* const* it = GetOrders(aStart);
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i < len; ++i, ++it) {
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aChain->AppendElement(MakeResourceAcquisition(*it));
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if (GetDeductionChain_Helper(*it, aTarget, aChain))
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return true;
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aChain->RemoveElementAt(aChain->Length() - 1);
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}
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return false;
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}
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/**
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* The partial order on resource acquisitions used by the deadlock
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* detector.
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*/
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PLHashTable* mOrdering; // T* -> PLHashEntry<OrderingEntry>
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/**
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* Protects contentious methods.
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* Nb: can't use mozilla::Mutex since we are used as its deadlock
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* detector.
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*/
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PRLock* mLock;
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private:
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DeadlockDetector(const DeadlockDetector& aDD) MOZ_DELETE;
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DeadlockDetector& operator=(const DeadlockDetector& aDD) MOZ_DELETE;
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};
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template<typename T>
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const PLHashAllocOps DeadlockDetector<T>::kAllocOps = {
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DeadlockDetector<T>::TableAlloc, DeadlockDetector<T>::TableFree,
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DeadlockDetector<T>::EntryAlloc, DeadlockDetector<T>::EntryFree
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};
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template<typename T>
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// FIXME bug 456272: tune based on average workload
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const uint32_t DeadlockDetector<T>::kDefaultNumBuckets = 64;
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} // namespace mozilla
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#endif // ifndef mozilla_DeadlockDetector_h
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