From: Tejun Heo <tj@kernel.org>
To: Andrea Righi <arighi@nvidia.com>
Cc: sched-ext@lists.linux.dev, David Vernet <void@manifault.com>,
Changwoo Min <changwoo@igalia.com>,
Emil Tsalapatis <emil@etsalapatis.com>,
David Dai <david.dai@linux.dev>,
linux-kernel@vger.kernel.org, Sashiko <sashiko-bot@kernel.org>
Subject: Re: [PATCH 19/17] sched_ext: Fix the stall watchdog blaming a bypassing owner for a stuck task
Date: Mon, 26 Oct 2026 11:31:32 -1000 [thread overview]
Message-ID: <3e758373745216d349e2d70afb42b7b8@kernel.org> (raw)
In-Reply-To: <at4l0yXTk7T_ouk0@gpd4>
Hello, Andrea.
On Sun, Oct 25, 2026 at 04:52:51PM +0100, Andrea Righi wrote:
> Should we recheck watchdog_timeout after changing sch?
>
> The stall test above uses the task owner's timeout. So, a bypassing
> child with a short timeout could potentially cause its host to be
> ejected before the host's own timeout expires.
Yes, and the same mismatch is already in the dsq->sched blame that
2c91169377f4 ("sched_ext: Blame the DSQ's owning scheduler for a
runnable stall") added, which is in v7.3.
The blame doesn't need the DSQ at all. scx_exec_sched() gives the sched
running the task: the owner, or its host while the owner is bypassing.
That covers both the bypass DSQ case and the rescue/local DSQ case this
patch handles. The watchdog blames that sched and uses that sched's
timeout for the stall test.
The task's wait also carries across a bypass move. It waited under the
owner and then gets charged to the host, or the other way around when
bypass lifts. The fix restarts the wait when scx_bypass() requeues a
task, except for the root's own tasks.
So, I'm dropping this patch and will post the fix on its own for
sched_ext/for-7.4-fixes with a stable Cc.
Thanks.
--
tejun
next prev parent reply other threads:[~2026-10-26 21:31 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-23 17:55 [PATCHSET v3 sched_ext/for-7.4] sched_ext: Fix bypassed sub-scheduler tasks stalling when the host lacks caps Tejun Heo
2026-10-23 17:55 ` [PATCH 01/17] sched_ext: Pack scx_ent_flags' multi-bit fields at the top Tejun Heo
2026-10-23 17:55 ` [PATCH 02/17] sched_ext: Clear holding_cpu where the claim is confirmed Tejun Heo
2026-10-23 17:55 ` [PATCH 03/17] sched_ext: Fix bypassed tasks stranded by the reenqueue limit Tejun Heo
2026-10-23 17:55 ` [PATCH 04/17] sched_ext: Fix bypassed tasks looping on a host without SCX_CAP_ENQ Tejun Heo
2026-10-23 18:50 ` sashiko-bot
2026-10-23 19:08 ` Tejun Heo
2026-10-23 17:55 ` [PATCH 05/17] sched_ext: Move refill_task_slice_dfl() below apply_slice_vtime() Tejun Heo
2026-10-23 17:55 ` [PATCH 06/17] sched_ext: Fix rescue served time disagreeing with the slice under proxy execution Tejun Heo
2026-10-23 17:55 ` [PATCH 07/17] sched_ext: Restore a rescuee's slice after ops.stopping() Tejun Heo
2026-10-23 17:55 ` [PATCH 08/17] sched_ext: Fix a cpu idling with a runnable rescuee Tejun Heo
2026-10-23 17:56 ` [PATCH 09/17] sched_ext: Mark the rescue grant as a kernel slice with SCX_TASK_KERNEL_SLICE Tejun Heo
2026-10-23 17:56 ` [PATCH 10/17] sched_ext: Refuse extending a kernel slice Tejun Heo
2026-10-23 17:56 ` [PATCH 11/17] sched_ext: Fix a cpu idling after put_prev_task_scx() queues its task on the local DSQ Tejun Heo
2026-10-23 17:56 ` [PATCH 12/17] sched_ext: Expire prev's slice in dispatch_one() under bypass Tejun Heo
2026-10-23 17:56 ` [PATCH 13/17] sched_ext: Fix bypassed tasks stalling when the host lacks SCX_CAP_BASE Tejun Heo
2026-10-23 19:02 ` sashiko-bot
2026-10-23 20:06 ` Tejun Heo
2026-10-23 17:56 ` [PATCH 14/17] sched_ext: Fix the bypass load balancer stranding tasks on cpus where " Tejun Heo
2026-10-23 17:56 ` [PATCH 15/17] sched_ext: Factor out bypass_lb_move() and insert with the donor DSQ unlocked Tejun Heo
2026-10-23 17:56 ` [PATCH 16/17] sched_ext: Let the bypass load balancer move tasks homed on other cpus Tejun Heo
2026-10-23 17:56 ` [PATCH 17/17] sched_ext: Fix queued bypassed tasks stalling when the host loses SCX_CAP_BASE Tejun Heo
2026-10-25 15:47 ` Andrea Righi
2026-10-26 21:31 ` Tejun Heo
2026-10-23 20:06 ` [PATCH 18/17] sched_ext: Fix use-after-free of a NONE rescuee leaving sched_ext Tejun Heo
2026-10-23 20:06 ` [PATCH 19/17] sched_ext: Fix the stall watchdog blaming a bypassing owner for a stuck task Tejun Heo
2026-10-25 15:52 ` Andrea Righi
2026-10-26 21:31 ` Tejun Heo [this message]
2026-10-23 20:10 ` [PATCH 20/17] sched_ext: Fix a lone IMMED task waiting behind a kept prev Tejun Heo
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