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lockding/lockdep: Avoid to find wrong lock dep path in check_irq_usage()

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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
This commit is contained in:
Boqun Feng 2021-06-19 01:01:09 +08:00 committed by Peter Zijlstra
parent d4c157c7b1
commit 7b1f8c6179
1 changed files with 11 additions and 1 deletions
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12
kernel/locking/lockdep.c
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@ -2768,8 +2768,18 @@ 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)) {