For some reason I cannot find the patch in my inbox. I can only see the
reply from Andrew and this notification email.
On Mon 03-09-18 16:22:31, Andrew Morton wrote:
> From: KJ Tsanaktsidis <ktsanaktsidis@xxxxxxxxxxx>
> Subject: fork: report pid exhaustion correctly
>
> Make the clone and fork syscalls return EAGAIN when the limit on the
> number of pids /proc/sys/kernel/pid_max is exceeded.
>
> Currently, when the pid_max limit is exceeded, the kernel will return
> ENOSPC from the fork and clone syscalls. This is contrary to the
> documented behaviour, which explicitly calls out the pid_max case as one
> where EAGAIN should be returned. It also leads to really confusing error
> messages in userspace programs which will complain about a lack of disk
> space when they fail to create processes/threads for this reason.
>
> This error is being returned because alloc_pid() uses the idr api to find
> a new pid; when there are none available, idr_alloc_cyclic() returns
> -ENOSPC, and this is being propagated back to userspace.
>
> This behaviour has been broken before, and was explicitly fixed in
> commit 35f71bc0a09a ("fork: report pid reservation failure properly"),
> so I think -EAGAIN is definitely the right thing to return in this case.
> The current behaviour change dates from commit 95846ecf9dac ("pid:
> replace pid bitmap implementation with IDR AIP") and was I believe
> unintentional.
Yeah, ENOSPC just doesn't make any sense.
> This patch has no impact on the case where allocating a pid fails because
> the child reaper for the namespace is dead; that case will still return
> -ENOMEM.
>
> Link: http://lkml.kernel.org/r/20180903111016.46461-1-ktsanaktsidis@xxxxxxxxxxx
> Fixes: 95846ecf9dac ("pid: replace pid bitmap implementation with IDR AIP")
> Signed-off-by: KJ Tsanaktsidis <ktsanaktsidis@xxxxxxxxxxx>
> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Gargi Sharma <gs051095@xxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
>
>
> diff -puN kernel/pid.c~fork-report-pid-exhaustion-correctly kernel/pid.c
> --- a/kernel/pid.c~fork-report-pid-exhaustion-correctly
> +++ a/kernel/pid.c
> @@ -195,7 +195,7 @@ struct pid *alloc_pid(struct pid_namespa
> idr_preload_end();
>
> if (nr < 0) {
> - retval = nr;
> + retval = (nr == -ENOSPC) ? -EAGAIN : nr;
> goto out_free;
> }
>
> _
>
> Patches currently in -mm which might be from ktsanaktsidis@xxxxxxxxxxx are
>
> fork-report-pid-exhaustion-correctly.patch
--
Michal Hocko
SUSE Labs
