Commit-ID: eca1a08986f622c11b75b3b44d561a1f901c9cec
Gitweb: http://git.kernel.org/tip/eca1a08986f622c11b75b3b44d561a1f901c9cec
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 23 Oct 2014 11:41:22 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed, 29 Oct 2014 10:07:04 -0700
signal: Exit RCU read-side critical section on each pass through loop
The kill_pid_info() can potentially loop indefinitely if tasks are created
and deleted sufficiently quickly, and if this happens, this function
will remain in a single RCU read-side critical section indefinitely.
This commit therefore exits the RCU read-side critical section on each
pass through the loop. Because a race must happen to retry the loop,
this should have no performance impact in the common case.
Reported-by: Dave Jones <davej@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reviewed-by: Pranith Kumar <bobby.prani@xxxxxxxxx>
---
kernel/signal.c | 30 ++++++++++++++----------------
1 file changed, 14 insertions(+), 16 deletions(-)
diff --git a/kernel/signal.c b/kernel/signal.c
index 8f0876f..5482098 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1331,23 +1331,21 @@ int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
int error = -ESRCH;
struct task_struct *p;
- rcu_read_lock();
-retry:
- p = pid_task(pid, PIDTYPE_PID);
- if (p) {
- error = group_send_sig_info(sig, info, p);
- if (unlikely(error == -ESRCH))
- /*
- * The task was unhashed in between, try again.
- * If it is dead, pid_task() will return NULL,
- * if we race with de_thread() it will find the
- * new leader.
- */
- goto retry;
- }
- rcu_read_unlock();
+ for (;;) {
+ rcu_read_lock();
+ p = pid_task(pid, PIDTYPE_PID);
+ if (p)
+ error = group_send_sig_info(sig, info, p);
+ rcu_read_unlock();
+ if (likely(!p || error != -ESRCH))
+ return error;
- return error;
+ /*
+ * The task was unhashed in between, try again. If it
+ * is dead, pid_task() will return NULL, if we race with
+ * de_thread() it will find the new leader.
+ */
+ }
}
int kill_proc_info(int sig, struct siginfo *info, pid_t pid)
--
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