This is a note to let you know that I've just added the patch titled
uprobes: Remove too strict lockdep_assert() condition in hprobe_expire()
to the 6.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
uprobes-remove-too-strict-lockdep_assert-condition-i.patch
and it can be found in the queue-6.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 45e07f5f34a46ee8451994c2e4de5442abaa9251
Author: Andrii Nakryiko <andrii@xxxxxxxxxx>
Date: Tue Feb 25 14:32:14 2025 -0800
uprobes: Remove too strict lockdep_assert() condition in hprobe_expire()
[ Upstream commit f8c857238a392f21d5726d07966f6061007c8d4f ]
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: dd1a7567784e ("uprobes: SRCU-protect uretprobe lifetime (with timeout)")
Reported-by: Breno Leitao <leitao@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20250225223214.2970740-1-andrii@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index e11e2df50a3ee..3c34761c9ae73 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -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) {
