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| author | Tejun Heo <tj@kernel.org> | 2026-05-10 23:08:16 +0300 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2026-05-10 23:08:16 +0300 |
| commit | c941d7391f258d5d06e0f7e962a52f99a547a83e (patch) | |
| tree | 8c8e7475a6b19be4b6ed61faf7b24f7db3a4f51b /include/linux | |
| parent | cceb8fa9cb2cf98e31d81ecf6353b6ba5ac57744 (diff) | |
| download | linux-c941d7391f258d5d06e0f7e962a52f99a547a83e.tar.xz | |
sched_ext: Close root-enable vs sched_ext_dead() race with SCX_TASK_INIT_BEGIN
scx_root_enable_workfn() drops the iter rq lock for ops.init_task() and a
TASK_DEAD @p can fall through sched_ext_dead() in that window. The race hits
when sched_ext_dead() observes SCX_TASK_INIT (the intermediate state before
@p->scx.sched is published) and dereferences NULL via SCX_HAS_OP(NULL,
exit_task), or observes SCX_TASK_NONE during the unlocked init window and
skips cleanup so exit_task() never runs.
Add SCX_TASK_INIT_BEGIN. The enable path writes NONE -> INIT_BEGIN under the
iter rq lock, then takes the rq lock again after init to walk INIT_BEGIN ->
INIT -> READY. sched_ext_dead() that wins the rq-lock race observes
INIT_BEGIN and sets DEAD without calling into ops; the post-init recheck
unwinds via scx_sub_init_cancel_task().
scx_fork() runs single-threaded against sched_ext_dead() (the task is not on
scx_tasks until scx_post_fork() adds it) so its INIT_BEGIN -> INIT walk
needs no rq-lock pairing; it rolls back to NONE on ops.init_task() failure.
The validation matrix grows the INIT_BEGIN row and the INIT_BEGIN -> DEAD
edge; INIT now requires INIT_BEGIN as the predecessor. scx_sub_disable()'s
migration writes INIT_BEGIN as a synthetic predecessor to satisfy the
tightened verification.
The sub-sched paths still race with sched_ext_dead() during the unlocked
init window. This will be fixed by the next patch.
Reported-by: zhidao su <suzhidao@xiaomi.com>
Link: https://lore.kernel.org/all/20260429133155.3825247-1-suzhidao@xiaomi.com/
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/sched/ext.h | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h index 9f1a326ad03e..2129e18ada58 100644 --- a/include/linux/sched/ext.h +++ b/include/linux/sched/ext.h @@ -106,6 +106,7 @@ enum scx_ent_flags { * Bits 8 to 10 are used to carry task state: * * NONE ops.init_task() not called yet + * INIT_BEGIN ops.init_task() in flight; see sched_ext_dead() * INIT ops.init_task() succeeded, but task can be cancelled * READY fully initialized, but not in sched_ext * ENABLED fully initialized and in sched_ext @@ -116,10 +117,11 @@ enum scx_ent_flags { SCX_TASK_STATE_MASK = ((1 << SCX_TASK_STATE_BITS) - 1) << SCX_TASK_STATE_SHIFT, SCX_TASK_NONE = 0 << SCX_TASK_STATE_SHIFT, - SCX_TASK_INIT = 1 << SCX_TASK_STATE_SHIFT, - SCX_TASK_READY = 2 << SCX_TASK_STATE_SHIFT, - SCX_TASK_ENABLED = 3 << SCX_TASK_STATE_SHIFT, - SCX_TASK_DEAD = 4 << SCX_TASK_STATE_SHIFT, + SCX_TASK_INIT_BEGIN = 1 << SCX_TASK_STATE_SHIFT, + SCX_TASK_INIT = 2 << SCX_TASK_STATE_SHIFT, + SCX_TASK_READY = 3 << SCX_TASK_STATE_SHIFT, + SCX_TASK_ENABLED = 4 << SCX_TASK_STATE_SHIFT, + SCX_TASK_DEAD = 5 << SCX_TASK_STATE_SHIFT, /* * Bits 12 and 13 are used to carry reenqueue reason. In addition to |