Pull KCSAN updates from Paul McKenney:
- improve the documentation for the new __data_racy type qualifier
to the data_race() macro's kernel-doc header and to the LKMM's
access-marking documentation
- add missing MODULE_DESCRIPTION
* tag 'kcsan.2024.07.12a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
kcsan: Add missing MODULE_DESCRIPTION() macro
kcsan: Add example to data_race() kerneldoc header
Code reorganization for the lock.cat file in tools/memory-model:
Improve the efficiency by ruling out right at the start RU events
(spin_is_locked() calls that return False) inside a critical section
for the same lock.
Improve the organization of the code for handling LF and RU events by
pulling the definitions of the pair-to-relation macro out from two
different complicated compound expressions, using a single standalone
definition instead.
Rewrite the calculations of the rf relation for LF and RU events, for
greater clarity.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Andrea reported that the following innocuous litmus test:
C T
{}
P0(spinlock_t *x)
{
int r0;
spin_lock(x);
spin_unlock(x);
r0 = spin_is_locked(x);
}
gives rise to a nonsensical empty result with no executions:
$ herd7 -conf linux-kernel.cfg T.litmus
Test T Required
States 0
Ok
Witnesses
Positive: 0 Negative: 0
Condition forall (true)
Observation T Never 0 0
Time T 0.00
Hash=6fa204e139ddddf2cb6fa963bad117c0
The problem is caused by a bug in the lock.cat part of the LKMM. Its
computation of the rf relation for RU (read-unlocked) events is
faulty; it implicitly assumes that every RU event must read from
either a UL (unlock) event in another thread or from the lock's
initial state. Neither is true in the litmus test above, so the
computation yields no possible executions.
The lock.cat code tries to make up for this deficiency by allowing RU
events outside of critical sections to read from the last po-previous
UL event. But it does this incorrectly, trying to keep these rfi links
separate from the rfe links that might also be needed, and passing only
the latter to herd7's cross() macro.
The problem is fixed by merging the two sets of possible rf links for
RU events and using them all in the call to cross().
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrea Parri <parri.andrea@gmail.com>
Closes: https://lore.kernel.org/linux-arch/ZlC0IkzpQdeGj+a3@andrea/
Tested-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Fixes: 15553dcbca ("tools/memory-model: Add model support for spin_is_locked()")
CC: <stable@vger.kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Given that access-marking.txt exists, this commit makes it easier to find.
Reported-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Although the data_race() kerneldoc header accurately states what it does,
some of the implications and usage patterns are non-obvious. Therefore,
add a brief locking example and also state how to have KCSAN ignore
accesses while also preventing the compiler from folding, spindling,
or otherwise mutilating the access.
[ paulmck: Apply Bart Van Assche feedback. ]
[ paulmck: Apply feedback from Marco Elver. ]
Reported-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Jens Axboe <axboe@kernel.dk>
Pull Linux Kernel Memory Model scripting updates from Paul McKenney:
"This improves litmus-test documentation and improves the ability to do
before/after tests on the https://github.com/paulmckrcu/litmus repo"
* tag 'lkmm-scripting.2023.04.07a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (32 commits)
tools/memory-model: Remove out-of-date SRCU documentation
tools/memory-model: Document LKMM test procedure
tools/memory-model: Use "grep -E" instead of "egrep"
tools/memory-model: Use "-unroll 0" to keep --hw runs finite
tools/memory-model: Make judgelitmus.sh handle scripted Result: tag
tools/memory-model: Add data-race capabilities to judgelitmus.sh
tools/memory-model: Add checktheselitmus.sh to run specified litmus tests
tools/memory-model: Repair parseargs.sh header comment
tools/memory-model: Add "--" to parseargs.sh for additional arguments
tools/memory-model: Make history-check scripts use mselect7
tools/memory-model: Make checkghlitmus.sh use mselect7
tools/memory-model: Fix scripting --jobs argument
tools/memory-model: Implement --hw support for checkghlitmus.sh
tools/memory-model: Add -v flag to jingle7 runs
tools/memory-model: Make runlitmus.sh check for jingle errors
tools/memory-model: Allow herd to deduce CPU type
tools/memory-model: Keep assembly-language litmus tests
tools/memory-model: Move from .AArch64.litmus.out to .litmus.AArch.out
tools/memory-model: Make runlitmus.sh generate .litmus.out for --hw
tools/memory-model: Split runlitmus.sh out of checklitmus.sh
...
Commit 6cd244c87428 ("tools/memory-model: Provide exact SRCU semantics")
changed the semantics of partially overlapping SRCU read-side critical
sections (among other things), making such documentation out-of-date.
The new, semantic changes are discussed in explanation.txt. Remove the
out-of-date documentation.
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit documents how to run the various scripts in order to test
a potentially pervasive change to the memory model.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The latest version of grep claims the egrep is now obsolete so the build
now contains warnings that look like:
egrep: warning: egrep is obsolescent; using grep -E
fix this up by moving the related file to use "grep -E" instead.
sed -i "s/egrep/grep -E/g" `grep egrep -rwl tools/memory-model`
Here are the steps to install the latest grep:
wget http://ftp.gnu.org/gnu/grep/grep-3.8.tar.gz
tar xf grep-3.8.tar.gz
cd grep-3.8 && ./configure && make
sudo make install
export PATH=/usr/local/bin:$PATH
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Litmus tests involving atomic operations produce LL/SC loops on a number
of architectures, and unrolling these loops can result in excessive
verification times or even stack overflows. This commit therefore uses
the "-unroll 0" herd7 argument to avoid unrolling, on the grounds that
additional passes through an LL/SC loop should not change the verification.
Note however, that certain bugs in the mapping of the LL/SC loop to
machine instructions may go undetected. On the other hand, herd7 might
not be the best vehicle for finding such bugs in any case. (You do
stress-test your architecture-specific code, don't you?)
Suggested-by: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The scripts that generate the litmus tests in the "auto" directory of
the https://github.com/paulmckrcu/litmus archive place the "Result:"
tag into a single-line ocaml comment, which judgelitmus.sh currently
does not recognize. This commit therefore makes judgelitmus.sh
recognize both the multiline comment format that it currently does
and the automatically generated single-line format.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds functionality to judgelitmus.sh to allow it to handle
both the "DATARACE" markers in the "Result:" comments in litmus tests
and the "Flag data-race" markers in LKMM output. For C-language tests,
if either marker is present, the other must also be as well, at least for
litmus tests having a "Result:" comment. If the LKMM output indicates
a data race, then failures of the Always/Sometimes/Never portion of the
"Result:" prediction are forgiven.
The reason for forgiving "Result:" mispredictions is that data races can
result in "interesting" compiler optimizations, so that all bets are off
in the data-race case.
[ paulmck: Apply Akira Yokosawa feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a checktheselitmus.sh script that runs the litmus tests
specified on the command line. This is useful for verifying fixes to
specific litmus tests.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, parseargs.sh expects to consume all the command-line arguments,
which prevents the calling script from having any of its own arguments.
This commit therefore causes parseargs.sh to stop consuming arguments
when it encounters a "--" argument, leaving any remaining arguments for
the calling script.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The history-check scripts currently use grep to ignore non-C-language
litmus tests, which is a bit fragile. This commit therefore enlists the
aid of "mselect7 -arch C", given Luc Maraget's recent modifications that
allow mselect7 to operate in filter mode.
This change requires herdtools 7.52-32-g1da3e0e50977 or later.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The checkghlitmus.sh script currently uses grep to ignore non-C-language
litmus tests, which is a bit fragile. This commit therefore enlists the
aid of "mselect7 -arch C", given Luc Maraget's recent modifications that
allow mselect7 to operate in filter mode.
This change requires herdtools 7.52-32-g1da3e0e50977 or later.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The parseargs.sh regular expression for the --jobs argument incorrectly
requires that the number of jobs be at least 10, that is, have at least
two digits. This commit therefore adjusts this regular expression to
allow single-digit numbers of jobs to be specified.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commits enables the "--hw" argument for the checkghlitmus.sh script,
causing it to convert any applicable C-language litmus tests to the
specified flavor of assembly language, to verify these assembly-language
litmus tests, and checking compatibility of the outcomes.
Note that the conversion does not yet handle locking, RCU, SRCU, plain
C-language memory accesses, or casts.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Adding the -v flag to jingle7 invocations gives much useful information
on why jingle7 didn't like a given litmus test. This commit therefore
adds this flag and saves off any such information into a .err file.
Suggested-by: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
It turns out that the jingle7 tool is currently a bit picky about
the litmus tests it is willing to process. This commit therefore
ensures that jingle7 failures are reported.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, the scripts specify the CPU's .cat file to herd. But this is
pointless because herd will select a good and sufficient .cat file from
the assembly-language litmus test itself. This commit therefore removes
the -model argument to herd, allowing herd to figure the CPU family out
itself.
Note that the user can override herd's choice using the "--herdopts"
argument to the scripts.
Suggested-by: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit retains the assembly-language litmus tests generated from
the C-language litmus tests, appending the hardware tag to the original
C-language litmus test's filename. Thus, S+poonceonces.litmus.AArch64
contains the Armv8 assembly language corresponding to the C-language
S+poonceonces.litmus test.
This commit also updates the .gitignore to avoid committing these
automatically generated assembly-language litmus tests.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
When the github scripts see ".litmus.out", they assume that there must be
a corresponding C-language ".litmus" file. Won't they be disappointed
when they instead see nothing, or, worse yet, the corresponding
assembly-language litmus test? This commit therefore swaps the hardware
tag with the "litmus" to avoid this sort of disappointment.
This commit also adjusts the .gitignore file so as to avoid adding these
new ".out" files to git.
[ paulmck: Apply Akira Yokosawa feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
