Subject: [merged] exitc-call-proc_exit_connector-after-exit_state-is-set.patch removed from -mm tree
To: guillaume@xxxxxxxxxxx,davem@xxxxxxxxxxxxx,matt.helsley@xxxxxxxxx,oleg@xxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 08 Apr 2014 14:15:44 -0700
The patch titled
Subject: kernel/exit.c: call proc_exit_connector() after exit_state is set
has been removed from the -mm tree. Its filename was
exitc-call-proc_exit_connector-after-exit_state-is-set.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Guillaume Morin <guillaume@xxxxxxxxxxx>
Subject: kernel/exit.c: call proc_exit_connector() after exit_state is set
The process events connector delivers a notification when a process exits.
This is really convenient for a process that spawns and wants to monitor
its children through an epoll-able() interface.
Unfortunately, there is a small window between when the event is delivered
and the child become wait()-able.
This is creates a race if the parent wants to make sure that it knows
about the exit, e.g
pid_t pid = fork();
if (pid > 0) {
register_interest_for_pid(pid);
if (waitpid(pid, NULL, WNOHANG) > 0)
{
/* We might have raced with exit() */
}
return;
}
/* Child */
execve(...)
register_interest_for_pid() would be telling the the connector socket
reader to pay attention to events related to pid.
Though this is not a bug, I think it would make the connector a bit more
usable if this race was closed by simply moving the call to
proc_exit_connector() from just before exit_notify() to right after.
Oleg said:
: Even with this patch the code above is still "racy" if the child is
: multi-threaded. Plus it should obviously filter-out subthreads. And
: afaics there is no way to make it reliable, even if you change the code
: above so that waitpid() is called only after the last thread exits WNOHANG
: still can fail.
Signed-off-by: Guillaume Morin <guillaume@xxxxxxxxxxx>
Cc: Matt Helsley <matt.helsley@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/exit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN kernel/exit.c~exitc-call-proc_exit_connector-after-exit_state-is-set kernel/exit.c
--- a/kernel/exit.c~exitc-call-proc_exit_connector-after-exit_state-is-set
+++ a/kernel/exit.c
@@ -802,13 +802,13 @@ void do_exit(long code)
module_put(task_thread_info(tsk)->exec_domain->module);
- proc_exit_connector(tsk);
/*
* FIXME: do that only when needed, using sched_exit tracepoint
*/
flush_ptrace_hw_breakpoint(tsk);
exit_notify(tsk, group_dead);
+ proc_exit_connector(tsk);
#ifdef CONFIG_NUMA
task_lock(tsk);
mpol_put(tsk->mempolicy);
_
Patches currently in -mm which might be from guillaume@xxxxxxxxxxx are
origin.patch
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