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author | Guillaume Morin <guillaume@morinfr.org> | 2014-04-07 15:38:31 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-04-07 16:36:04 -0700 |
commit | ef9823939e5acd5d323ff61fbc427ef998dd203e (patch) | |
tree | 84685216b295fa81ea71af435889f040af3fcf1f /kernel | |
parent | 4bcb8232cf4eb061b086c10f56b6808adcdb5a93 (diff) | |
download | linux-ef9823939e5acd5d323ff61fbc427ef998dd203e.tar.gz linux-ef9823939e5acd5d323ff61fbc427ef998dd203e.tar.bz2 linux-ef9823939e5acd5d323ff61fbc427ef998dd203e.zip |
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@morinfr.org>
Cc: Matt Helsley <matt.helsley@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/exit.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/exit.c b/kernel/exit.c index 171c9a9d7b00..decf648574f6 100644 --- a/kernel/exit.c +++ b/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); |