From: Boqun Feng boqun.feng@gmail.com
[ Upstream commit 7b1f8c6179769af6ffa055e1169610b51d71edd5 ]
In the step #3 of check_irq_usage(), we seach backwards to find a lock whose usage conflicts the usage of @target_entry1 on safe/unsafe. However, we should only keep the irq-unsafe usage of @target_entry1 into consideration, because it could be a case where a lock is hardirq-unsafe but soft-safe, and in check_irq_usage() we find it because its hardirq-unsafe could result into a hardirq-safe-unsafe deadlock, but currently since we don't filter out the other usage bits, so we may find a lock dependency path softirq-unsafe -> softirq-safe, which in fact doesn't cause a deadlock. And this may cause misleading lockdep splats.
Fix this by only keeping LOCKF_ENABLED_IRQ_ALL bits when we try the backwards search.
Reported-by: Johannes Berg johannes@sipsolutions.net Signed-off-by: Boqun Feng boqun.feng@gmail.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lore.kernel.org/r/20210618170110.3699115-4-boqun.feng@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/locking/lockdep.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 78b51b8ad4f6..788629c06ce9 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -2764,8 +2764,18 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev, * Step 3: we found a bad match! Now retrieve a lock from the backward * list whose usage mask matches the exclusive usage mask from the * lock found on the forward list. + * + * Note, we should only keep the LOCKF_ENABLED_IRQ_ALL bits, considering + * the follow case: + * + * When trying to add A -> B to the graph, we find that there is a + * hardirq-safe L, that L -> ... -> A, and another hardirq-unsafe M, + * that B -> ... -> M. However M is **softirq-safe**, if we use exact + * invert bits of M's usage_mask, we will find another lock N that is + * **softirq-unsafe** and N -> ... -> A, however N -> .. -> M will not + * cause a inversion deadlock. */ - backward_mask = original_mask(target_entry1->class->usage_mask); + backward_mask = original_mask(target_entry1->class->usage_mask & LOCKF_ENABLED_IRQ_ALL);
ret = find_usage_backwards(&this, backward_mask, &target_entry); if (bfs_error(ret)) {