diff options
| author | Tejun Heo <tj@kernel.org> | 2026-07-12 07:23:55 -1000 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2026-07-15 05:00:53 -1000 |
| commit | fadeedd7cfc5d73d33fa3d7ac54b9b27aabd09d2 (patch) | |
| tree | d5a217654145ad87d9160474589d921909bbbdbe /include/linux | |
| parent | 97fef602584458b100d383afed9d176c0bc689ab (diff) | |
sched/psi: Create the psimon kthread outside of cgroup_mutex
a5b98009f16d ("sched/psi: fix race between file release and pressure write")
made pressure_write() hold cgroup_mutex across psi_trigger_create(), which
forks the psimon kthread for the first rtpoll trigger. As kthread creation
depends on the whole fork path, the commit inadvertently created a lot of
unwanted locking dependencies from cgroup_mutex.
sched_ext got hit by one: its enable path blocks forks and then grabs
cgroup_mutex, so a pressure write racing a scheduler enable deadlocks, with
every other fork piling up behind.
Fix it by splitting trigger creation so that the worker is forked with
cgroup_mutex dropped and the kernfs active reference left broken. The latter
matters because rmdir and cgroup.pressure writes drain active references
under cgroup_mutex. Publishing the trigger last keeps error reporting
synchronous and preserves the of->priv lifetime rules.
The trigger registered in the first stage pins the group's rtpoll machinery
across the unlocked window, leaving only creation races to resolve. The
catch-up poll on installation covers scheduling attempts dropped while there
was no worker.
v2: Retagged sched/psi (was cgroup).
Fixes: a5b98009f16d ("sched/psi: fix race between file release and pressure write")
Cc: stable@vger.kernel.org
Cc: Edward Adam Davis <eadavis@qq.com>
Cc: Chen Ridong <chenridong@huaweicloud.com>
Reported-by: Matt Fleming <mfleming@cloudflare.com>
Closes: https://lore.kernel.org/all/20260710100441.2653477-1-matt@readmodwrite.com/
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Matt Fleming <mfleming@cloudflare.com>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/psi.h | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/psi.h b/include/linux/psi.h index e0745873e3f2..7966e3ac03b9 100644 --- a/include/linux/psi.h +++ b/include/linux/psi.h @@ -25,7 +25,9 @@ void psi_memstall_leave(unsigned long *flags); int psi_show(struct seq_file *s, struct psi_group *group, enum psi_res res); struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, enum psi_res res, struct file *file, - struct kernfs_open_file *of); + struct kernfs_open_file *of, + bool *need_rtpoll_worker); +int psi_trigger_create_rtpoll_worker(struct psi_group *group); void psi_trigger_destroy(struct psi_trigger *t); __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file, |