linux-stable.git/kernel/sched, branch v6.18.47

futex: Fix might_sleep() warning in futex_pivot_pending()

2026-08-27T12:32:54+00:00

commit d8aa5dd97944a72d4a9e3cc79bb80fcac7d6e829 upstream.

A younger me put a WARN in might_sleep() to warn about nested sleep loops. This
younger me also build a wait-loop variant that can deal with it. This wait-loop
variant doesn't have all the fancy wrappers, since it isn't used much. It also
lacks wait-bit support.

Add the wait-bit support and use it to fix the nested wait issue.

Fixes: 8e7ff730dd96 ("futex: Fix race in futex_pivot_pending() during private hash resize")
Reported-by: syzbot+350a93852ac854927f45@syzkaller.appspotmail.com
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20260820074927.GH1246887@noisy.programming.kicks-ass.net
Closes: https://syzkaller.appspot.com/bug?extid=350a93852ac854927f45
Signed-off-by: Greg Kroah-Hartman

sched_ext: Take cgroup_lock() first in scx_cgroup_lock()

2026-08-23T12:27:05+00:00

[ Upstream commit 5f8b69642d18e1f3e11996707842ac530444e959 ]

scx_cgroup_lock() write-locks scx_cgroup_ops_rwsem and then takes
cgroup_lock(), which can deadlock through kernfs:

  scx enable/disable         cgroup rmdir           cpu.weight write
  ------------------         ------------           ----------------
                             cgroup_lock()
  percpu_down_write(rwsem)
  cgroup_lock()
                                                    kernfs_get_active()
                                                    percpu_down_read(rwsem)
                             kernfs_drain()

The enable path waits for the rmdir to release cgroup_mutex. The rmdir,
deactivating the cpu controller's files, waits in kernfs_drain() for the
write's active reference. The write, in scx_group_set_weight(), waits for
the rwsem behind the pending writer.

Take cgroup_lock() first. The set_* paths take no cgroup locks inside the
read side, so a pending write-lock then only waits for read sections that
always run to completion, and no dependency from the rwsem back to
cgroup_mutex remains.

Fixes: a5bd6ba30b33 ("sched_ext: Use cgroup_lock/unlock() to synchronize against cgroup operations")
Cc: stable@vger.kernel.org # v6.18+
Signed-off-by: Tejun Heo 
Reviewed-by: Andrea Righi 
[ dropped the `#ifdef CONFIG_EXT_GROUP_SCHED` guards since the code already sits inside one, and applied to kernel/sched/ext.c instead of kernel/sched/ext/ext.c ]
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

sched_ext: Reorganize enable/disable path for multi-scheduler support

2026-08-23T12:27:05+00:00

[ Upstream commit dbd542a8fac7bcfba91e353f2a522e1bf2fbee27 ]

In preparation for multiple scheduler support, reorganize the enable and
disable paths to make scheduler instances explicit. Extract
scx_root_disable() from scx_disable_workfn(). Rename scx_enable_workfn()
to scx_root_enable_workfn(). Change scx_disable() to take @sch parameter
and only queue disable_work if scx_claim_exit() succeeds for consistency.
Move exit_kind validation into scx_claim_exit(). The sysrq handler now
prints a message when no scheduler is loaded.

These changes don't materially affect user-visible behavior.

v2: Keep scx_enable() name as-is and only rename the workfn to
    scx_root_enable_workfn(). Change scx_enable() return type to s32.

Signed-off-by: Tejun Heo 
Reviewed-by: Andrea Righi 
Stable-dep-of: 5f8b69642d18 ("sched_ext: Take cgroup_lock() first in scx_cgroup_lock()")
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

sched_ext: Update p->scx.disallow warning in scx_init_task()

2026-08-23T12:27:05+00:00

[ Upstream commit 0454a604b98a9bf301e82860cd216ec4ac563668 ]

- Always trigger the warning if p->scx.disallow is set for fork inits. There
  is no reason to set it during forks.

- Flip the positions of if/else arms to ease adding error conditions.

Signed-off-by: Tejun Heo 
Reviewed-by: Andrea Righi 
Stable-dep-of: 5f8b69642d18 ("sched_ext: Take cgroup_lock() first in scx_cgroup_lock()")
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

sched/psi: Create the psimon kthread outside of cgroup_mutex

2026-08-19T16:18:20+00:00

commit fadeedd7cfc5d73d33fa3d7ac54b9b27aabd09d2 upstream.

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 
Cc: Chen Ridong 
Reported-by: Matt Fleming 
Closes: https://lore.kernel.org/all/20260710100441.2653477-1-matt@readmodwrite.com/
Signed-off-by: Tejun Heo 
Acked-by: Johannes Weiner 
Tested-by: Matt Fleming 
Acked-by: Suren Baghdasaryan 
Signed-off-by: Greg Kroah-Hartman

sched/psi: Shut down rtpoll_timer in psi_cgroup_free()

2026-08-19T16:18:20+00:00

commit 5457025fa8ca3c0d2732109513de839e3e797190 upstream.

psi_schedule_rtpoll_work() is called locklessly from the scheduler hotpath
and can race psi_trigger_destroy() taking down the last rtpoll trigger under
rtpoll_trigger_lock:

  psi_schedule_rtpoll_work()        psi_trigger_destroy()

  rcu_read_lock();
  task = rcu_dereference(rtpoll_task);
                                    rcu_assign_pointer(rtpoll_task, NULL);
                                    timer_delete(&rtpoll_timer);
  mod_timer(&rtpoll_timer, ...);
  rcu_read_unlock();
                                    synchronize_rcu();
                                    kthread_stop(task_to_destroy);

The group can then be freed with the re-armed timer still pending, and
poll_timer_fn() runs on freed memory.

461daba06bdc ("psi: eliminate kthread_worker from psi trigger scheduling
mechanism") deleted the timer synchronously after the synchronize_rcu(),
which prevented this but raced trigger creation instead: the deletion could
cancel the timer that a new trigger set armed during the grace period and,
as creation also reinitialized the timer at the time, corrupt it.
8f91efd870ea ("psi: Fix race between psi_trigger_create/destroy") moved the
initialization into group_init() and the deletion into the locked section,
trading the creation races for the window above.

Neither placement in the destruction path works. A pending timer firing
while the group is alive is harmless though. poll_timer_fn() just wakes the
rtpoll waitqueue and doesn't re-arm itself. Bind the timer to the group's
lifetime instead and shut it down in psi_cgroup_free(). Nothing can arm it
by then. timer_shutdown_sync() because the timer is never armed again.

Fixes: 8f91efd870ea ("psi: Fix race between psi_trigger_create/destroy")
Cc: stable@vger.kernel.org # v5.10+
Reported-by: Sashiko AI 
Closes: https://lore.kernel.org/all/20260711000434.36C4A1F000E9@smtp.kernel.org/
Signed-off-by: Tejun Heo 
Acked-by: Johannes Weiner 
Tested-by: Matt Fleming 
Acked-by: Suren Baghdasaryan 
Signed-off-by: Greg Kroah-Hartman

sched/fair: Revert 6d71a9c61604 ("sched/fair: Fix EEVDF entity placement bug causing scheduling lag")

2026-08-19T16:17:12+00:00

[ Upstream commit 101f3498b4bdfef97152a444847948de1543f692 ]

Zicheng Qu reported that, because avg_vruntime() always includes
cfs_rq->curr, when ->on_rq, place_entity() doesn't work right.

Specifically, the lag scaling in place_entity() relies on
avg_vruntime() being the state *before* placement of the new entity.
However in this case avg_vruntime() will actually already include the
entity, which breaks things.

Also, Zicheng Qu argues that avg_vruntime should be invariant under
reweight. IOW commit 6d71a9c61604 ("sched/fair: Fix EEVDF entity
placement bug causing scheduling lag") was wrong!

The issue reported in 6d71a9c61604 could possibly be explained by
rounding artifacts -- notably the extreme weight '2' is outside of the
range of avg_vruntime/sum_w_vruntime, since that uses
scale_load_down(). By scaling vruntime by the real weight, but
accounting it in vruntime with a factor 1024 more, the average moves
significantly. However, that is now cured.

Tested by reverting 66951e4860d3 ("sched/fair: Fix update_cfs_group()
vs DELAY_DEQUEUE") and tracing vruntime and vlag figures again.

Reported-by: Zicheng Qu 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Vincent Guittot 
Tested-by: K Prateek Nayak 
Tested-by: Shubhang Kaushik 
Link: https://patch.msgid.link/20260219080625.066102672%40infradead.org
(cherry picked from commit 101f3498b4bdfef97152a444847948de1543f692)
[jstultz: Resolved minor collision in the revert against 6.18-stable]
Signed-off-by: John Stultz 
Signed-off-by: Sasha Levin

cpufreq: schedutil: Publish util hooks only after all sg_cpu are initialized

2026-08-09T18:25:19+00:00

commit f0a3f042293a8c5a2152346b3637ea60866c503a upstream.

Commit 16a03c71bba0 ("cpufreq: schedutil: Merge initialization code of
sg_cpu in single loop") merged the per-CPU initialization and the
utilization-hook registration into a single loop in sugov_start().

For a shared cpufreq policy this re-introduces the race originally fixed
by commit ab2f7cf141aa ("cpufreq: schedutil: Fix sugov_start() versus
sugov_update_shared() race").

The scheduler's util path reaches the hook under RCU-sched and never takes
policy->rwsem, so the rwsem held across sugov_start() cannot serialize the
two. Once the first CPU's hook is published, sugov_update_shared() may run
and, via sugov_next_freq_shared(), read/write each sibling sugov_cpu
(iowait_boost, util, bw_min, ...) concurrently with the memset() still
initializing them, with no lock common to both sides: the update side holds
sg_policy->update_lock while the init side holds only policy->rwsem, which
the scheduler's util path never takes.

The walk only accesses scalar members, never a pointer like ->sg_policy,
so it does not crash today; it merely uses stale (or zero on first start)
values that skew the frequency selection and tracepoints. It is still a
genuine data race, and a latent crash once any pointer member is
dereferenced there.

Restore the two-phase approach: initialize all per-CPU structures first,
and only then publish the per-CPU utilization update hooks.

Fixes: 16a03c71bba0 ("cpufreq: schedutil: Merge initialization code of sg_cpu in single loop")
Cc: stable@vger.kernel.org
Signed-off-by: Zhongqiu Han 
Reviewed-by: Christian Loehle 
Link: https://patch.msgid.link/20260716115159.848403-1-zhongqiu.han@oss.qualcomm.com
Signed-off-by: Rafael J. Wysocki 
Signed-off-by: Greg Kroah-Hartman

sched/deadline: Use revised wakeup rule only for running dl_server

2026-08-09T18:25:09+00:00

[ Upstream commit 1842bf97af109f5ebf830175c9725bf81ebb78b1 ]

Commit 14a857056466 ("sched/deadline: Use revised wakeup rule for
dl_server") applies the revised wakeup rule to any server, as a result
servers that are not running (dl_defer_running == 0) and start with a
deadline overflow get enqueued and can boost tasks as if they were
running, invalidating the defer rule and the documented state model.

Apply the revised wakeup rule only for deferrable servers that are
marked as running.

Fixes: 14a857056466 ("sched/deadline: Use revised wakeup rule for dl_server")
Signed-off-by: Gabriele Monaco 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Juri Lelli 
Tested-by: Andrea Righi 
Link: https://patch.msgid.link/20260522125833.264145-1-gmonaco@redhat.com
Signed-off-by: Sasha Levin

sched_ext: Don't warn on core-sched forced idle in put_prev_task_scx()

2026-08-03T09:21:28+00:00

[ Upstream commit b7d9c359e5cf867f7eb23df3bb1c6b9e58af24da ]

put_prev_task_scx() warns when a runnable task drops to a lower sched_class
without SCX_OPS_ENQ_LAST, on the assumption that balance_one() would have
kept it running. Core scheduling breaks that: a forced-idle SMT sibling
reschedules through the core_pick fast path in pick_next_task(), which skips
pick_task_scx() and thus balance_one(), so a runnable task can drop to idle
with ENQ_LAST unset.

Gate the warning on sched_cpu_cookie_match(): a cookie mismatch means core
scheduling forced the idle, while a match (or core scheduling off) still
catches a genuine missing-ENQ_LAST drop.

Fixes: 7c65ae81ea86 ("sched_ext: Don't call put_prev_task_scx() before picking the next task")
Signed-off-by: Tejun Heo 
Reviewed-by: Andrea Righi 
Signed-off-by: Sasha Levin