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signal: Exit RCU read-side critical section on each pass through loop

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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@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
This commit is contained in:
Paul E. McKenney 2014-10-23 11:41:22 -07:00
commit eca1a08986
1 changed files with 14 additions and 16 deletions
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30
kernel/signal.c
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@ -1331,23 +1331,21 @@ int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
int error = -ESRCH; int error = -ESRCH;
struct task_struct *p; struct task_struct *p;
rcu_read_lock(); for (;;) {
retry: rcu_read_lock();
p = pid_task(pid, PIDTYPE_PID); p = pid_task(pid, PIDTYPE_PID);
if (p) { if (p)
error = group_send_sig_info(sig, info, p); error = group_send_sig_info(sig, info, p);
if (unlikely(error == -ESRCH)) rcu_read_unlock();
/* if (likely(!p || error != -ESRCH))
* The task was unhashed in between, try again. return error;
* 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();
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) int kill_proc_info(int sig, struct siginfo *info, pid_t pid)