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Tejun Heo
fadeedd7cf
a5b98009f1("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:a5b98009f1("sched/psi: fix race between file release and pressure write") Cc: [email protected] Cc: Edward Adam Davis <[email protected]> Cc: Chen Ridong <[email protected]> Reported-by: Matt Fleming <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Signed-off-by: Tejun Heo <[email protected]> Acked-by: Johannes Weiner <[email protected]> Tested-by: Matt Fleming <[email protected]> Acked-by: Suren Baghdasaryan <[email protected]>