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 -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html