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@zendesk.com 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@zendesk.com Fixes: 95846ecf9dac ("pid: replace pid bitmap implementation with IDR AIP") Signed-off-by: KJ Tsanaktsidis ktsanaktsidis@zendesk.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Michal Hocko mhocko@suse.cz Cc: Gargi Sharma gs051095@gmail.com Cc: Rik van Riel riel@redhat.com Cc: Oleg Nesterov oleg@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
Acked-by: Michal Hocko mhocko@suse.com
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@zendesk.com are
fork-report-pid-exhaustion-correctly.patch