6.13-stable review patch. If anyone has any objections, please let me know.
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From: Andrii Nakryiko andrii@kernel.org
[ 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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/uprobes.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
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) {