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uprobes: Remove too strict lockdep_assert() condition in hprobe_expire()

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hprobe_expire() is used to atomically switch pending uretprobe instance
(struct return_instance) from being SRCU protected to be refcounted.
This can be done from background timer thread, or synchronously within
current thread when task is forked.

In the former case, return_instance has to be protected through RCU read
lock, and that's what hprobe_expire() used to check with
lockdep_assert(rcu_read_lock_held()).

But in the latter case (hprobe_expire() called from dup_utask()) there
is no RCU lock being held, and it's both unnecessary and incovenient.
Inconvenient due to the intervening memory allocations inside
dup_return_instance()'s loop. Unnecessary because dup_utask() is called
synchronously in current thread, and no uretprobe can run at that point,
so return_instance can't be freed either.

So drop rcu_read_lock_held() condition, and expand corresponding comment
to explain necessary lifetime guarantees. lockdep_assert()-detected
issue is a false positive.

Fixes: dd1a756778 ("uprobes: SRCU-protect uretprobe lifetime (with timeout)")
Reported-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250225223214.2970740-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2025-02-25 14:32:14 -08:00 • committed by Ingo Molnar
parent 68a9b0e313
commit f8c857238a
1 changed files with 7 additions and 3 deletions
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10
kernel/events/uprobes.c
View file

@ -767,10 +767,14 @@ static struct uprobe *hprobe_expire(struct hprobe *hprobe, bool get)
enum hprobe_state hstate;
/*
* return_instance's hprobe is protected by RCU.
* Underlying uprobe is itself protected from reuse by SRCU.
* Caller should guarantee that return_instance is not going to be
* freed from under us. This can be achieved either through holding
* rcu_read_lock() or by owning return_instance in the first place.
*
* Underlying uprobe is itself protected from reuse by SRCU, so ensure
* SRCU lock is held properly.
*/
lockdep_assert(rcu_read_lock_held() && srcu_read_lock_held(&uretprobes_srcu));
lockdep_assert(srcu_read_lock_held(&uretprobes_srcu));
hstate = READ_ONCE(hprobe->state);
switch (hstate) {