Commit 82f3b142 authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
Browse files

rqspinlock: Fix TAS fallback lock entry creation 



The TAS fallback can be invoked directly when queued spin locks are
disabled, and through the slow path when paravirt is enabled for queued
spin locks. In the latter case, the res_spin_lock macro will attempt the
fast path and already hold the entry when entering the slow path. This
will lead to creation of extraneous entries that are not released, which
may cause false positives for deadlock detection.

Fix this by always preceding invocation of the TAS fallback in every
case with the grabbing of the held lock entry, and add a comment to make
note of this.

Fixes: c9102a68 ("rqspinlock: Add a test-and-set fallback")
Reported-by: default avatarAmery Hung <ameryhung@gmail.com>
Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Tested-by: default avatarAmery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/r/20260122115911.3668985-1-memxor@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent a32ae265

include/asm-generic/rqspinlock.h

+1 −1
Original line number Diff line number Diff line
@@ -191,7 +191,7 @@ static __always_inline int res_spin_lock(rqspinlock_t *lock) 


#else



#define res_spin_lock(lock) resilient_tas_spin_lock(lock)

#define res_spin_lock(lock) ({ grab_held_lock_entry(lock); resilient_tas_spin_lock(lock); })



#endif /* CONFIG_QUEUED_SPINLOCKS */

kernel/bpf/rqspinlock.c

+4 −3
Original line number Diff line number Diff line
@@ -265,10 +265,11 @@ int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock) 


	RES_INIT_TIMEOUT(ts);

	/*

	 * The fast path is not invoked for the TAS fallback, so we must grab

	 * the deadlock detection entry here.

	 * We are either called directly from res_spin_lock after grabbing the

	 * deadlock detection entry when queued spinlocks are disabled, or from

	 * resilient_queued_spin_lock_slowpath after grabbing the deadlock

	 * detection entry. No need to obtain it here.

	 */

	grab_held_lock_entry(lock);



	/*

	 * Since the waiting loop's time is dependent on the amount of