sched: Fix psi_dequeue for Proxy Execution

Currently, if the sleep flag is set, psi_dequeue() doesn't change any of the psi_flags.

This is because psi_switch_task() will clear TSK_ONCPU as well as other potential flags (TSK_RUNNING), and the assumption is that a voluntary sleep always consists of a task being dequeued followed shortly there after with a psi_sched_switch() call.

Proxy Execution changes this expectation, as mutex-blocked tasks that would normally sleep stay on the runqueue. But in the case where the mutex-owning task goes to sleep, or the owner is on a remote cpu, we will then deactivate the blocked task shortly after.

In that situation, the mutex-blocked task will have had its TSK_ONCPU cleared when it was switched off the cpu, but it will stay TSK_RUNNING. Then if we later dequeue it (as currently done if we hit a case find_proxy_task() can't yet handle, such as the case of the owner being on another rq or a sleeping owner) psi_dequeue() won't change any state (leaving it TSK_RUNNING), as it incorrectly expects a psi_task_switch() call to immediately follow.

Later on when the task get woken/re-enqueued, and psi_flags are
set for TSK_RUNNING, we hit an error as the task is already
TSK_RUNNING:
psi: inconsistent task state! task=188:kworker/28:0 cpu=28 psi_flags=4 clear=0 set=4

To resolve this, extend the logic in psi_dequeue() so that if the sleep flag is set, we also check if psi_flags have TSK_ONCPU set (meaning the psi_task_switch is imminent) before we do the shortcut return.

If TSK_ONCPU is not set, that means we've already switched away, and this psi_dequeue call needs to clear the flags.

Fixes be41bde4c3a8 ("sched: Add an initial sketch of the find_proxy_task() function")

Reported-by K Prateek Nayak <[email protected]>

Closes https://lore.kernel.org/lkml/[email protected]/ open here

Signed-off-by John Stultz <[email protected]>

Tested-by K Prateek Nayak <[email protected]>

---
v13:
* Reworked for collision
v15:
* Fixed commit message typo noticed by Todd Kjos v24:
* Reworded commit message in response to K Prateek pointing out this issue can affect us earlier in the full proxy series then I had anticipated.

Cc Joel Fernandes <[email protected]>

Cc Qais Yousef <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc Peter Zijlstra <[email protected]>

Cc Juri Lelli <[email protected]>

Cc Vincent Guittot <[email protected]>

Cc Dietmar Eggemann <[email protected]>

Cc Valentin Schneider <[email protected]>

Cc Johannes Weiner <[email protected]>

Cc Suren Baghdasaryan <[email protected]>

Cc Steven Rostedt <[email protected]>

Cc Ben Segall <[email protected]>

Cc Zimuzo Ezeozue <[email protected]>

Cc Mel Gorman <[email protected]>

Cc Will Deacon <[email protected]>

Cc Waiman Long <[email protected]>

Cc Boqun Feng <[email protected]>

Cc "Paul E. McKenney" <[email protected]>

Cc Metin Kaya <[email protected]>

Cc Xuewen Yan <[email protected]>

Cc K Prateek Nayak <[email protected]>

Cc Thomas Gleixner <[email protected]>

Cc Daniel Lezcano <[email protected]>

Cc Suleiman Souhlal <[email protected]>

Cc kuyo chang <[email protected]>

Cc hupu <[email protected]>

Cc [email protected]

---
 kernel/sched/stats.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

kernel/sched/stats.h +0 -0

index 26f3fd4d34cea..a38459813b537 100644