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 35f71bc0 ("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 95846ecf ("pid: replace pid bitmap implementation with IDR AIP") and was I believe unintentional. 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: 95846ecf ("pid: replace pid bitmap implementation with IDR AIP") Signed-off-by:KJ Tsanaktsidis <ktsanaktsidis@zendesk.com> Reviewed-by:
Andrew Morton <akpm@linux-foundation.org> Acked-by:
Michal Hocko <mhocko@suse.com> 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> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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ae596de1
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