The following commit has been merged into the perf/urgent branch of tip: Commit-ID: f8c857238a392f21d5726d07966f6061007c8d4f Gitweb: https://git.kernel.org/tip/f8c857238a392f21d5726d07966f6061007c8d4f Author: Andrii Nakryiko <andrii@xxxxxxxxxx> AuthorDate: Tue, 25 Feb 2025 14:32:14 -08:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Tue, 25 Feb 2025 23:36:19 +01:00 uprobes: Remove too strict lockdep_assert() condition in hprobe_expire() 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 --- 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 af53fbd..b4ca889 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) {
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