Messages in this thread Patch in this message | | | From | ktsanaktsidis@zendesk ... | Subject | [PATCH] fork: report pid exhaustion correctly | Date | Mon, 3 Sep 2018 04:10:16 -0700 |
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From: KJ Tsanaktsidis <ktsanaktsidis@zendesk.com>
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 the alloc_pid function uses the idr api to find a new pid; when there are none available, idr_alloc_cyclic is returns -ENOSPC, and this is being propagated back into 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.
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.
Fixes: 95846ecf9dac ("pid: replace pid bitmap implementation with IDR AIP") Signed-off-by: KJ Tsanaktsidis <ktsanaktsidis@zendesk.com> --- kernel/pid.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/pid.c b/kernel/pid.c index de1cfc4f75a2..cdf63e53a014 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -195,7 +195,7 @@ struct pid *alloc_pid(struct pid_namespace *ns) idr_preload_end(); if (nr < 0) { - retval = nr; + retval = (nr == -ENOSPC) ? -EAGAIN : nr; goto out_free; } -- 2.17.1
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