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locking/lockdep: Add debug_locks check in __lock_downgrade()
authorWaiman Long <longman@redhat.com>
Thu, 10 Jan 2019 04:03:25 +0000 (23:03 -0500)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 5 Oct 2019 10:27:39 +0000 (12:27 +0200)
commit2a8d47d551f3fd68d45b1564f1915343d8d26777
tree999735880b9b286626a38640d5ecd7b81e391950
parent3fea925a915ac7469c890a16d4fa45fc9ed531e5
locking/lockdep: Add debug_locks check in __lock_downgrade()

[ Upstream commit 513e1073d52e55b8024b4f238a48de7587c64ccf ]

Tetsuo Handa had reported he saw an incorrect "downgrading a read lock"
warning right after a previous lockdep warning. It is likely that the
previous warning turned off lock debugging causing the lockdep to have
inconsistency states leading to the lock downgrade warning.

Fix that by add a check for debug_locks at the beginning of
__lock_downgrade().

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot+53383ae265fb161ef488@syzkaller.appspotmail.com
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/1547093005-26085-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
kernel/locking/lockdep.c