Syzbot has reported that it can hit a NULL pointer dereference in
wb_workfn() due to wb->bdi->dev being NULL. This indicates that
wb_workfn() was called for an already unregistered bdi which should not
happen as wb_shutdown() called from bdi_unregister() should make sure
all pending writeback works are completed before bdi is unregistered.
Except that wb_workfn() itself can requeue the work with:
mod_delayed_work(bdi_wq, &wb->dwork, 0);
and if this happens while wb_shutdown() is waiting in:
flush_delayed_work(&wb->dwork);
the dwork can get executed after wb_shutdown() has finished and
bdi_unregister() has cleared wb->bdi->dev.
Make wb_workfn() use wakeup_wb() for requeueing the work which takes all
the necessary precautions against racing with bdi unregistration.
CC: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
CC: Tejun Heo <tj@kernel.org>
Fixes: 839a8e8660
Reported-by: syzbot <syzbot+9873874c735f2892e7e9@syzkaller.appspotmail.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
lock_page_memcg()/unlock_page_memcg() use spin_lock_irqsave/restore() if
the page's memcg is undergoing move accounting, which occurs when a
process leaves its memcg for a new one that has
memory.move_charge_at_immigrate set.
unlocked_inode_to_wb_begin,end() use spin_lock_irq/spin_unlock_irq() if
the given inode is switching writeback domains. Switches occur when
enough writes are issued from a new domain.
This existing pattern is thus suspicious:
lock_page_memcg(page);
unlocked_inode_to_wb_begin(inode, &locked);
...
unlocked_inode_to_wb_end(inode, locked);
unlock_page_memcg(page);
If both inode switch and process memcg migration are both in-flight then
unlocked_inode_to_wb_end() will unconditionally enable interrupts while
still holding the lock_page_memcg() irq spinlock. This suggests the
possibility of deadlock if an interrupt occurs before unlock_page_memcg().
truncate
__cancel_dirty_page
lock_page_memcg
unlocked_inode_to_wb_begin
unlocked_inode_to_wb_end
<interrupts mistakenly enabled>
<interrupt>
end_page_writeback
test_clear_page_writeback
lock_page_memcg
<deadlock>
unlock_page_memcg
Due to configuration limitations this deadlock is not currently possible
because we don't mix cgroup writeback (a cgroupv2 feature) and
memory.move_charge_at_immigrate (a cgroupv1 feature).
If the kernel is hacked to always claim inode switching and memcg
moving_account, then this script triggers lockup in less than a minute:
cd /mnt/cgroup/memory
mkdir a b
echo 1 > a/memory.move_charge_at_immigrate
echo 1 > b/memory.move_charge_at_immigrate
(
echo $BASHPID > a/cgroup.procs
while true; do
dd if=/dev/zero of=/mnt/big bs=1M count=256
done
) &
while true; do
sync
done &
sleep 1h &
SLEEP=$!
while true; do
echo $SLEEP > a/cgroup.procs
echo $SLEEP > b/cgroup.procs
done
The deadlock does not seem possible, so it's debatable if there's any
reason to modify the kernel. I suggest we should to prevent future
surprises. And Wang Long said "this deadlock occurs three times in our
environment", so there's more reason to apply this, even to stable.
Stable 4.4 has minor conflicts applying this patch. For a clean 4.4 patch
see "[PATCH for-4.4] writeback: safer lock nesting"
https://lkml.org/lkml/2018/4/11/146
Wang Long said "this deadlock occurs three times in our environment"
[gthelen@google.com: v4]
Link: http://lkml.kernel.org/r/20180411084653.254724-1-gthelen@google.com
[akpm@linux-foundation.org: comment tweaks, struct initialization simplification]
Change-Id: Ibb773e8045852978f6207074491d262f1b3fb613
Link: http://lkml.kernel.org/r/20180410005908.167976-1-gthelen@google.com
Fixes: 682aa8e1a6 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates")
Signed-off-by: Greg Thelen <gthelen@google.com>
Reported-by: Wang Long <wanglong19@meituan.com>
Acked-by: Wang Long <wanglong19@meituan.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: <stable@vger.kernel.org> [v4.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
And use it in a few more places rather than opencoding the values.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This is a pure automated search-and-replace of the internal kernel
superblock flags.
The s_flags are now called SB_*, with the names and the values for the
moment mirroring the MS_* flags that they're equivalent to.
Note how the MS_xyz flags are the ones passed to the mount system call,
while the SB_xyz flags are what we then use in sb->s_flags.
The script to do this was:
# places to look in; re security/*: it generally should *not* be
# touched (that stuff parses mount(2) arguments directly), but
# there are two places where we really deal with superblock flags.
FILES="drivers/mtd drivers/staging/lustre fs ipc mm \
include/linux/fs.h include/uapi/linux/bfs_fs.h \
security/apparmor/apparmorfs.c security/apparmor/include/lib.h"
# the list of MS_... constants
SYMS="RDONLY NOSUID NODEV NOEXEC SYNCHRONOUS REMOUNT MANDLOCK \
DIRSYNC NOATIME NODIRATIME BIND MOVE REC VERBOSE SILENT \
POSIXACL UNBINDABLE PRIVATE SLAVE SHARED RELATIME KERNMOUNT \
I_VERSION STRICTATIME LAZYTIME SUBMOUNT NOREMOTELOCK NOSEC BORN \
ACTIVE NOUSER"
SED_PROG=
for i in $SYMS; do SED_PROG="$SED_PROG -e s/MS_$i/SB_$i/g"; done
# we want files that contain at least one of MS_...,
# with fs/namespace.c and fs/pnode.c excluded.
L=$(for i in $SYMS; do git grep -w -l MS_$i $FILES; done| sort|uniq|grep -v '^fs/namespace.c'|grep -v '^fs/pnode.c')
for f in $L; do sed -i $f $SED_PROG; done
Requested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Since commit 925a6efb8f ("Btrfs: stop using
try_to_writeback_inodes_sb_nr to flush delalloc") this function hasn't
been used outside so stop exporting it.
In addition we merge it into try_to_writeback_inodes_sb() which is the
only caller. Also change return type of try_to_writeback_inodes_sb to
void as the only user ext4 doesn't care.
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Handle start-all writeback like we do periodic or kupdate
style writeback - by marking the bdi_writeback as needing a full
flush, and simply waking the thread. This eliminates the need to
allocate and queue a specific work item just for this purpose.
After this change, we truly only ever have one of them running at
any point in time. We mark the need to start all flushes, and the
writeback thread will clear it once it has processed the request.
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When someone calls wakeup_flusher_threads() or
wakeup_flusher_threads_bdi(), they schedule writeback of all dirty
pages in the system (or on that bdi). If we are tight on memory, we
can get tons of these queued from kswapd/vmscan. This causes (at
least) two problems:
1) We consume a ton of memory just allocating writeback work items.
We've seen as much as 600 million of these writeback work items
pending. That's a lot of memory to pointlessly hold hostage,
while the box is under memory pressure.
2) We spend so much time processing these work items, that we
introduce a softlockup in writeback processing. This is because
each of the writeback work items don't end up doing any work (it's
hard when you have millions of identical ones coming in to the
flush machinery), so we just sit in a tight loop pulling work
items and deleting/freeing them.
Fix this by adding a 'start_all' bit to the writeback structure, and
set that when someone attempts to flush all dirty pages. The bit is
cleared when we start writeback on that work item. If the bit is
already set when we attempt to queue !nr_pages writeback, then we
simply ignore it.
This provides us one full flush in flight, with one pending as well,
and makes for more efficient handling of this type of writeback.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Chris Mason <clm@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Now that we have no external callers of wb_start_writeback(), we
can shuffle the passing in of 'nr_pages'. Everybody passes in 0
at this point, so just kill the argument and move the dirty
count retrieval to that function.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Chris Mason <clm@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
We don't have any callers outside of fs-writeback.c anymore,
make it private.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Chris Mason <clm@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Similar to wakeup_flusher_threads(), except that we only wake
up the flusher threads on the specified backing device.
No functional changes in this patch.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Chris Mason <clm@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
We're writing back the full range of dirty pages on the devices,
there's no point in making this special and not do normal range
cyclic writeback.
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Everybody is passing in 0 now, let's get rid of the argument.
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently the writeback statistics code uses a percpu counters to hold
various statistics. Furthermore we have 2 families of functions - those
which disable local irq and those which doesn't and whose names begin
with double underscore. However, they both end up calling
__add_wb_stats which in turn calls percpu_counter_add_batch which is
already irq-safe.
Exploiting this fact allows to eliminated the __wb_* functions since
they don't add any further protection than we already have.
Furthermore, refactor the wb_* function to call __add_wb_stat directly
without the irq-disabling dance. This will likely result in better
runtime of code which deals with modifying the stat counters.
While at it also document why percpu_counter_add_batch is in fact
preempt and irq-safe since at least 3 people got confused.
Link: http://lkml.kernel.org/r/1498029937-27293-1-git-send-email-nborisov@suse.com
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Sphinx gets confused when it finds identation without a
good reason for it and without a preceding blank line:
./fs/mpage.c:347: ERROR: Unexpected indentation.
./fs/namei.c:4303: ERROR: Unexpected indentation.
./fs/fs-writeback.c:2060: ERROR: Unexpected indentation.
No functional changes.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
When WB_registered flag is not set, wb_queue_work() skips queuing the
work, but does not perform the necessary clean up. In particular, if
work->auto_free is true, it should free the memory.
The leak condition can be reprouced by following these steps:
mount /dev/sdb /mnt/sdb
/* In qemu console: device_del sdb */
umount /dev/sdb
Above will result in a wb_queue_work() call on an unregistered wb and
thus leak memory.
Reported-by: John Sperbeck <jsperbeck@google.com>
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
I've found funny live-lock between raid10 barriers during resync and
memory controller hard limits. Inside mpage_readpages() task holds on to
its plug bio which blocks the barrier in raid10. Its memory cgroup have
no free memory thus the task goes into reclaimer but all reclaimable
pages are dirty and cannot be written because raid10 is rebuilding and
stuck on the barrier.
Common flush of such IO in schedule() never happens, because the caller
doesn't go to sleep.
Lock is 'live' because changing memory limit or killing tasks which
holds that stuck bio unblock whole progress.
That was what happened in 3.18.x but I see no difference in upstream
logic. Theoretically this might happen even without memory cgroup.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@fb.com>
wait_sb_inodes() currently does a walk of all inodes in the filesystem
to find dirty one to wait on during sync. This is highly inefficient
and wastes a lot of CPU when there are lots of clean cached inodes that
we don't need to wait on.
To avoid this "all inode" walk, we need to track inodes that are
currently under writeback that we need to wait for. We do this by
adding inodes to a writeback list on the sb when the mapping is first
tagged as having pages under writeback. wait_sb_inodes() can then walk
this list of "inodes under IO" and wait specifically just for the inodes
that the current sync(2) needs to wait for.
Define a couple helpers to add/remove an inode from the writeback list
and call them when the overall mapping is tagged for or cleared from
writeback. Update wait_sb_inodes() to walk only the inodes under
writeback due to the sync.
With this change, filesystem sync times are significantly reduced for
fs' with largely populated inode caches and otherwise no other work to
do. For example, on a 16xcpu 2GHz x86-64 server, 10TB XFS filesystem
with a ~10m entry inode cache, sync times are reduced from ~7.3s to less
than 0.1s when the filesystem is fully clean.
Link: http://lkml.kernel.org/r/1466594593-6757-2-git-send-email-bfoster@redhat.com
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Tested-by: Holger Hoffstätte <holger.hoffstaette@applied-asynchrony.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
