linux.git/kernel/locking/lockdep.c, branch v6.18.21

lockdep: Speed up lockdep_unregister_key() with expedited RCU synchronization

2025-07-15T04:57:29+00:00

lockdep_unregister_key() is called from critical code paths, including
sections where rtnl_lock() is held. For example, when replacing a qdisc
in a network device, network egress traffic is disabled while
__qdisc_destroy() is called for every network queue.

If lockdep is enabled, __qdisc_destroy() calls lockdep_unregister_key(),
which gets blocked waiting for synchronize_rcu() to complete.

For example, a simple tc command to replace a qdisc could take 13
seconds:

  # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1: mq
    real    0m13.195s
    user    0m0.001s
    sys     0m2.746s

During this time, network egress is completely frozen while waiting for
RCU synchronization.

Use synchronize_rcu_expedited() instead to minimize the impact on
critical operations like network connectivity changes.

This improves 10x the function call to tc, when replacing the qdisc for
a network card.

   # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1: mq
     real     0m1.789s
     user     0m0.000s
     sys      0m1.613s

[boqun: Fixed the comment and add more information for the temporary
workaround, and add TODO information for hazptr]

Reported-by: Erik Lundgren 
Signed-off-by: Breno Leitao 
Reviewed-by: Paul E. McKenney 
Reviewed-by: Eric Dumazet 
Signed-off-by: Boqun Feng 
Link: https://lore.kernel.org/r/20250321-lockdep-v1-1-78b732d195fb@debian.org

locking/lockdep: Avoid struct return in lock_stats()

2025-07-15T04:57:20+00:00

Returning a large structure from the lock_stats() function causes clang
to have multiple copies of it on the stack and copy between them, which
can end up exceeding the frame size warning limit:

kernel/locking/lockdep.c:300:25: error: stack frame size (1464) exceeds limit (1280) in 'lock_stats' [-Werror,-Wframe-larger-than]
  300 | struct lock_class_stats lock_stats(struct lock_class *class)

Change the calling conventions to directly operate on the caller's copy,
which apparently is what gcc does already.

Signed-off-by: Arnd Bergmann 
Signed-off-by: Boqun Feng 
Link: https://lore.kernel.org/r/20250610092941.2642847-1-arnd@kernel.org

locking/lockdep: Add number of dynamic keys to /proc/lockdep_stats

2025-05-06T16:34:43+00:00

There have been recent reports about running out of lockdep keys:

	MAX_LOCKDEP_KEYS too low!

One possible reason is that too many dynamic keys have been registered.
A possible culprit is the lockdep_register_key() call in qdisc_alloc()
of net/sched/sch_generic.c.

Currently, there is no way to find out how many dynamic keys have been
registered. Add such a stat to the /proc/lockdep_stats to get better
clarity.

Signed-off-by: Waiman Long 
Signed-off-by: Boqun Feng 
Signed-off-by: Ingo Molnar 
Cc: Bill Wendling 
Cc: Justin Stitt 
Cc: Nathan Chancellor 
Cc: Nick Desaulniers 
Cc: Peter Zijlstra 
Cc: Will Deacon 
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-4-boqun.feng@gmail.com

locking/lockdep: Prevent abuse of lockdep subclass

2025-05-06T16:34:35+00:00

To catch the code trying to use a subclass value >= MAX_LOCKDEP_SUBCLASSES (8),
add a DEBUG_LOCKS_WARN_ON() statement to notify the users that such a
large value is not allowed.

[ boqun: Reword the commit log with a more objective tone ]

Signed-off-by: Waiman Long 
Signed-off-by: Boqun Feng 
Signed-off-by: Ingo Molnar 
Cc: Bill Wendling 
Cc: Justin Stitt 
Cc: Nathan Chancellor 
Cc: Nick Desaulniers 
Cc: Peter Zijlstra 
Cc: Will Deacon 
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-3-boqun.feng@gmail.com

locking/lockdep: Move hlock_equal() to the respective #ifdeffery

2025-05-06T16:34:31+00:00

When hlock_equal() is unused, it prevents kernel builds with clang,
`make W=1` and CONFIG_WERROR=y, CONFIG_LOCKDEP=y and
CONFIG_LOCKDEP_SMALL=n:

  lockdep.c:2005:20: error: unused function 'hlock_equal' [-Werror,-Wunused-function]

Fix this by moving the function to the respective existing ifdeffery
for its the only user.

See also:

  6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions for W=1 build")

Fixes: 68e305678583 ("lockdep: Adjust check_redundant() for recursive read change")
Signed-off-by: Andy Shevchenko 
Signed-off-by: Boqun Feng 
Signed-off-by: Ingo Molnar 
Cc: Bill Wendling 
Cc: Justin Stitt 
Cc: Nathan Chancellor 
Cc: Nick Desaulniers 
Cc: Peter Zijlstra 
Cc: Waiman Long 
Cc: Will Deacon 
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-2-boqun.feng@gmail.com

locking/lockdep: Decrease nr_unused_locks if lock unused in zap_class()

2025-03-27T07:23:17+00:00

Currently, when a lock class is allocated, nr_unused_locks will be
increased by 1, until it gets used: nr_unused_locks will be decreased by
1 in mark_lock(). However, one scenario is missed: a lock class may be
zapped without even being used once. This could result into a situation
that nr_unused_locks != 0 but no unused lock class is active in the
system, and when `cat /proc/lockdep_stats`, a WARN_ON() will
be triggered in a CONFIG_DEBUG_LOCKDEP=y kernel:

  [...] DEBUG_LOCKS_WARN_ON(debug_atomic_read(nr_unused_locks) != nr_unused)
  [...] WARNING: CPU: 41 PID: 1121 at kernel/locking/lockdep_proc.c:283 lockdep_stats_show+0xba9/0xbd0

And as a result, lockdep will be disabled after this.

Therefore, nr_unused_locks needs to be accounted correctly at
zap_class() time.

Signed-off-by: Boqun Feng 
Signed-off-by: Ingo Molnar 
Reviewed-by: Waiman Long 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250326180831.510348-1-boqun.feng@gmail.com

locking/lockdep: Add kasan_check_byte() check in lock_acquire()

2025-03-07T23:55:04+00:00

KASAN instrumentation of lockdep has been disabled, as we don't need
KASAN to check the validity of lockdep internal data structures and
incur unnecessary performance overhead. However, the lockdep_map pointer
passed in externally may not be valid (e.g. use-after-free) and we run
the risk of using garbage data resulting in false lockdep reports.

Add kasan_check_byte() call in lock_acquire() for non kernel core data
object to catch invalid lockdep_map and print out a KASAN report before
any lockdep splat, if any.

Suggested-by: Marco Elver 
Signed-off-by: Waiman Long 
Signed-off-by: Boqun Feng 
Signed-off-by: Ingo Molnar 
Reviewed-by: Marco Elver 
Reviewed-by: Andrey Konovalov 
Link: https://lore.kernel.org/r/20250214195242.2480920-1-longman@redhat.com
Link: https://lore.kernel.org/r/20250307232717.1759087-7-boqun.feng@gmail.com

locking/lock_events: Add locking events for lockdep

2025-03-07T23:55:03+00:00

Add some lock events to lockdep to profile its behavior.

Signed-off-by: Waiman Long 
Signed-off-by: Boqun Feng 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20250307232717.1759087-5-boqun.feng@gmail.com

treewide: const qualify ctl_tables where applicable

2025-01-28T12:48:37+00:00

Add the const qualifier to all the ctl_tables in the tree except for
watchdog_hardlockup_sysctl, memory_allocation_profiling_sysctls,
loadpin_sysctl_table and the ones calling register_net_sysctl (./net,
drivers/inifiniband dirs). These are special cases as they use a
registration function with a non-const qualified ctl_table argument or
modify the arrays before passing them on to the registration function.

Constifying ctl_table structs will prevent the modification of
proc_handler function pointers as the arrays would reside in .rodata.
This is made possible after commit 78eb4ea25cd5 ("sysctl: treewide:
constify the ctl_table argument of proc_handlers") constified all the
proc_handlers.

Created this by running an spatch followed by a sed command:
Spatch:
    virtual patch

    @
    depends on !(file in "net")
    disable optional_qualifier
    @

    identifier table_name != {
      watchdog_hardlockup_sysctl,
      iwcm_ctl_table,
      ucma_ctl_table,
      memory_allocation_profiling_sysctls,
      loadpin_sysctl_table
    };
    @@

    + const
    struct ctl_table table_name [] = { ... };

sed:
    sed --in-place \
      -e "s/struct ctl_table .table = &uts_kern/const struct ctl_table *table = \&uts_kern/" \
      kernel/utsname_sysctl.c

Reviewed-by: Song Liu 
Acked-by: Steven Rostedt (Google)  # for kernel/trace/
Reviewed-by: Martin K. Petersen  # SCSI
Reviewed-by: Darrick J. Wong  # xfs
Acked-by: Jani Nikula 
Acked-by: Corey Minyard 
Acked-by: Wei Liu 
Acked-by: Thomas Gleixner 
Reviewed-by: Bill O'Donnell 
Acked-by: Baoquan He 
Acked-by: Ashutosh Dixit 
Acked-by: Anna Schumaker 
Signed-off-by: Joel Granados

lockdep: Move lockdep_assert_locked() under #ifdef CONFIG_PROVE_LOCKING

2024-12-19T22:04:03+00:00

When lockdep_assert_locked() is unused, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y, CONFIG_LOCKDEP=y and
CONFIG_PROVE_LOCKING=n:

  kernel/locking/lockdep.c:160:20: error: unused function 'lockdep_assert_locked' [-Werror,-Wunused-function]

Fix this by moving it under the respective ifdeffery.

See also commit 6863f5643dd7 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

[Boqun: add more config information of the error]

Signed-off-by: Andy Shevchenko 
Signed-off-by: Boqun Feng 
Link: https://lore.kernel.org/r/20241202193445.769567-1-andriy.shevchenko@linux.intel.com