| Message ID | 20240907100204.28609-1-felix.moessbauer@siemens.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3,1/1] io_uring/sqpoll: inherit cpumask of creating process | expand |
On Sat, 07 Sep 2024 12:02:04 +0200, Felix Moessbauer wrote: > The submit queue polling threads are userland threads that just never > exit to the userland. In case the creating task is part of a cgroup > with the cpuset controller enabled, the poller should also stay within > that cpuset. This also holds, as the poller belongs to the same cgroup > as the task that started it. > > With the current implementation, a process can "break out" of the > defined cpuset by creating sq pollers consuming CPU time on other CPUs, > which is especially problematic for realtime applications. > > [...] Applied, thanks! [1/1] io_uring/sqpoll: inherit cpumask of creating process commit: b7ed6d8ffd627a3de8b0e336996d0247a6535608 Best regards,
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c index 3b50dc9586d1..713be7c29388 100644 --- a/io_uring/sqpoll.c +++ b/io_uring/sqpoll.c @@ -289,7 +289,6 @@ static int io_sq_thread(void *data) if (sqd->sq_cpu != -1) { set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu)); } else { - set_cpus_allowed_ptr(current, cpu_online_mask); sqd->sq_cpu = raw_smp_processor_id(); }
The submit queue polling threads are userland threads that just never exit to the userland. In case the creating task is part of a cgroup with the cpuset controller enabled, the poller should also stay within that cpuset. This also holds, as the poller belongs to the same cgroup as the task that started it. With the current implementation, a process can "break out" of the defined cpuset by creating sq pollers consuming CPU time on other CPUs, which is especially problematic for realtime applications. Part of this problem was fixed in a5fc1441 by dropping the PF_NO_SETAFFINITY flag, but this only becomes effective after the first modification of the cpuset (i.e. the pollers cpuset is correct after the first update of the enclosing cgroups cpuset). By inheriting the cpuset of the creating tasks, we ensure that the poller is created with a cpumask that is a subset of the cgroups mask. Inheriting the creators cpumask is reasonable, as other userland tasks also inherit the mask. Fixes: 37d1e2e3642e ("io_uring: move SQPOLL thread io-wq forked worker") Cc: stable@vger.kernel.org # 6.1+ Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com> --- Changes since v2: - in v2 I accidentally sent the backport of this patch for v6.1. Will resend that once this one is accepted. Anyways, now we know that this also works on a v6.1 kernel. Changes since v1: - do not set poller thread cpuset in non-pinning case, as the default is already correct (the mask is inherited from the parent). - Remove incorrect term "kernel thread" from the commit message I tested this without pinning, explicit pinning of the parent task and non-all cgroup cpusets (and all combinations). Best regards, Felix Moessbauer Siemens AG io_uring/sqpoll.c | 1 - 1 file changed, 1 deletion(-)