| Message ID | 20250225223214.2970740-1-andrii@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [perf/core] uprobes: remove too strict lockdep_assert() condition in hprobe_expire() | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Tue, Feb 25, 2025 at 02:32:14PM -0800, Andrii Nakryiko wrote: > 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> lgtm Reviewed-by: Jiri Olsa <jolsa@kernel.org> jirka > --- > 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 e783da1d1762..4d2140cab7ec 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -762,10 +762,14 @@ 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) { > -- > 2.43.5 >
On 02/25, Andrii Nakryiko wrote: > > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -762,10 +762,14 @@ 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)); Reviewed-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index e783da1d1762..4d2140cab7ec 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -762,10 +762,14 @@ 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) {
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> --- kernel/events/uprobes.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)