Messages in this thread Patch in this message |  | | Date | Thu, 23 Oct 2014 13:24:44 -0700 | From | "Paul E. McKenney" <> | Subject | Re: rcu_preempt detected stalls. |
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On Thu, Oct 23, 2014 at 09:53:37PM +0200, Oleg Nesterov wrote: > On 10/23, Paul E. McKenney wrote: > > > > OK, so making each pass through the loop a separate RCU read-side critical > > section might be considered to be suppressing notification of an error > > condition? > > I agree, this change probably makes sense anyway. Personally I'd prefer > the version below (somehow I hate multiple unlock's), but I won't insist.
Your code, your rules. ;-)
But given this structure, why not use a for() loop replace the "goto retry" with an inverted condition and a "return error"? Maybe something like the following patch?
Thanx, Paul
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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@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/signal.c b/kernel/signal.c index 8f0876f9f6dd..54820984a872 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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