Messages in this thread Patch in this message | | | Date | Mon, 10 Feb 2014 05:33:08 -0800 | From | tip-bot for Oleg Nesterov <> | Subject | [tip:core/locking] lockdep: Don' t create the wrong dependency on hlock->check == 0 |
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Commit-ID: 1b5ff816cab708ba44c7d7b56b613516269eb577 Gitweb: http://git.kernel.org/tip/1b5ff816cab708ba44c7d7b56b613516269eb577 Author: Oleg Nesterov <oleg@redhat.com> AuthorDate: Mon, 20 Jan 2014 19:20:10 +0100 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Sun, 9 Feb 2014 21:18:57 +0100
lockdep: Don't create the wrong dependency on hlock->check == 0
Test-case:
DEFINE_MUTEX(m1); DEFINE_MUTEX(m2); DEFINE_MUTEX(mx);
void lockdep_should_complain(void) { lockdep_set_novalidate_class(&mx);
// m1 -> mx -> m2 mutex_lock(&m1); mutex_lock(&mx); mutex_lock(&m2); mutex_unlock(&m2); mutex_unlock(&mx); mutex_unlock(&m1);
// m2 -> m1 ; should trigger the warning mutex_lock(&m2); mutex_lock(&m1); mutex_unlock(&m1); mutex_unlock(&m2); }
this doesn't trigger any warning, lockdep can't detect the trivial deadlock.
This is because lock(&mx) correctly avoids m1 -> mx dependency, it skips validate_chain() due to mx->check == 0. But lock(&m2) wrongly adds mx -> m2 and thus m1 -> m2 is not created.
rcu_lock_acquire()->lock_acquire(check => 0) is fine due to read == 2, so currently only __lockdep_no_validate__ can trigger this problem.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Dave Jones <davej@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20140120182010.GA26498@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/locking/lockdep.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 8c85a0d..f7eba92 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -1936,12 +1936,12 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) for (;;) { int distance = curr->lockdep_depth - depth + 1; - hlock = curr->held_locks + depth-1; + hlock = curr->held_locks + depth - 1; /* * Only non-recursive-read entries get new dependencies * added: */ - if (hlock->read != 2) { + if (hlock->read != 2 && hlock->check) { if (!check_prev_add(curr, hlock, next, distance, trylock_loop)) return 0;
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