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McKenney" Cc: "A. Sverdlin" , Marco Elver , linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Will Deacon , Waiman Long , stable@vger.kernel.org, Adrian Freihofer Subject: Re: [PATCH RESEND] locking/spinlock/debug: Fix data-race in do_raw_write_lock Message-ID: References: <20250826102731.52507-1-alexander.sverdlin@siemens.com> <7325588b-189c-4825-a87f-5494b1230d7a@paulmck-laptop> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7325588b-189c-4825-a87f-5494b1230d7a@paulmck-laptop> On Tue, Aug 26, 2025 at 04:44:30AM -0700, Paul E. McKenney wrote: > On Tue, Aug 26, 2025 at 12:27:27PM +0200, A. Sverdlin wrote: > > From: Alexander Sverdlin > > > > KCSAN reports: > > > > BUG: KCSAN: data-race in do_raw_write_lock / do_raw_write_lock > > > > write (marked) to 0xffff800009cf504c of 4 bytes by task 1102 on cpu 1: > > do_raw_write_lock+0x120/0x204 > > _raw_write_lock_irq > > do_exit > > call_usermodehelper_exec_async > > ret_from_fork > > > > read to 0xffff800009cf504c of 4 bytes by task 1103 on cpu 0: > > do_raw_write_lock+0x88/0x204 > > _raw_write_lock_irq > > do_exit > > call_usermodehelper_exec_async > > ret_from_fork > > > > value changed: 0xffffffff -> 0x00000001 > > > > Reported by Kernel Concurrency Sanitizer on: > > CPU: 0 PID: 1103 Comm: kworker/u4:1 6.1.111 > > > > Commit 1a365e822372 ("locking/spinlock/debug: Fix various data races") has > > adressed most of these races, but seems to be not consistent/not complete. > > > > >From do_raw_write_lock() only debug_write_lock_after() part has been > > converted to WRITE_ONCE(), but not debug_write_lock_before() part. > > Do it now. > > > > Cc: stable@vger.kernel.org > > Fixes: 1a365e822372 ("locking/spinlock/debug: Fix various data races") > > Reported-by: Adrian Freihofer > > Acked-by: Waiman Long > > Signed-off-by: Alexander Sverdlin > > Reviewed-by: Paul E. McKenney > Thank you, I will queue this for future testing ans reviews. Alexander, is there any link to a kcsan splat that we can use? Thanks! Regards, Boqun > > --- > > There are still some inconsistencies remaining IMO: > > - lock->magic is sometimes accessed with READ_ONCE() even though it's only > > being plain-written; > > - debug_spin_unlock() and debug_write_unlock() both do WRITE_ONCE() on > > lock->owner and lock->owner_cpu, but examine them with plain read accesses. > > > > kernel/locking/spinlock_debug.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c > > index 87b03d2e41dbb..2338b3adfb55f 100644 > > --- a/kernel/locking/spinlock_debug.c > > +++ b/kernel/locking/spinlock_debug.c > > @@ -184,8 +184,8 @@ void do_raw_read_unlock(rwlock_t *lock) > > static inline void debug_write_lock_before(rwlock_t *lock) > > { > > RWLOCK_BUG_ON(lock->magic != RWLOCK_MAGIC, lock, "bad magic"); > > - RWLOCK_BUG_ON(lock->owner == current, lock, "recursion"); > > - RWLOCK_BUG_ON(lock->owner_cpu == raw_smp_processor_id(), > > + RWLOCK_BUG_ON(READ_ONCE(lock->owner) == current, lock, "recursion"); > > + RWLOCK_BUG_ON(READ_ONCE(lock->owner_cpu) == raw_smp_processor_id(), > > lock, "cpu recursion"); > > } > > > > -- > > 2.47.1 > >