This is a note to let you know that I've just added the patch titled
sched/core: Disable page allocation in task_tick_mm_cid()
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-core-disable-page-allocation-in-task_tick_mm_c.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 3c2218fd9d59b14e7a365fa96c3b22b6f1525d7b
Author: Waiman Long <longman@xxxxxxxxxx>
Date: Wed Oct 9 21:44:32 2024 -0400
sched/core: Disable page allocation in task_tick_mm_cid()
[ Upstream commit 73ab05aa46b02d96509cb029a8d04fca7bbde8c7 ]
With KASAN and PREEMPT_RT enabled, calling task_work_add() in
task_tick_mm_cid() may cause the following splat.
[ 63.696416] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
[ 63.696416] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 610, name: modprobe
[ 63.696416] preempt_count: 10001, expected: 0
[ 63.696416] RCU nest depth: 1, expected: 1
This problem is caused by the following call trace.
sched_tick() [ acquire rq->__lock ]
-> task_tick_mm_cid()
-> task_work_add()
-> __kasan_record_aux_stack()
-> kasan_save_stack()
-> stack_depot_save_flags()
-> alloc_pages_mpol_noprof()
-> __alloc_pages_noprof()
-> get_page_from_freelist()
-> rmqueue()
-> rmqueue_pcplist()
-> __rmqueue_pcplist()
-> rmqueue_bulk()
-> rt_spin_lock()
The rq lock is a raw_spinlock_t. We can't sleep while holding
it. IOW, we can't call alloc_pages() in stack_depot_save_flags().
The task_tick_mm_cid() function with its task_work_add() call was
introduced by commit 223baf9d17f2 ("sched: Fix performance regression
introduced by mm_cid") in v6.4 kernel.
Fortunately, there is a kasan_record_aux_stack_noalloc() variant that
calls stack_depot_save_flags() while not allowing it to allocate
new pages. To allow task_tick_mm_cid() to use task_work without
page allocation, a new TWAF_NO_ALLOC flag is added to enable calling
kasan_record_aux_stack_noalloc() instead of kasan_record_aux_stack()
if set. The task_tick_mm_cid() function is modified to add this new flag.
The possible downside is the missing stack trace in a KASAN report due
to new page allocation required when task_work_add_noallloc() is called
which should be rare.
Fixes: 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20241010014432.194742-1-longman@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index cf5e7e891a776..2964171856e00 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -14,11 +14,14 @@ init_task_work(struct callback_head *twork, task_work_func_t func)
}
enum task_work_notify_mode {
- TWA_NONE,
+ TWA_NONE = 0,
TWA_RESUME,
TWA_SIGNAL,
TWA_SIGNAL_NO_IPI,
TWA_NMI_CURRENT,
+
+ TWA_FLAGS = 0xff00,
+ TWAF_NO_ALLOC = 0x0100,
};
static inline bool task_work_pending(struct task_struct *task)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9b406d9886541..b6f922a20f83a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -12050,7 +12050,9 @@ void task_tick_mm_cid(struct rq *rq, struct task_struct *curr)
return;
if (time_before(now, READ_ONCE(curr->mm->mm_cid_next_scan)))
return;
- task_work_add(curr, work, TWA_RESUME);
+
+ /* No page allocation under rq lock */
+ task_work_add(curr, work, TWA_RESUME | TWAF_NO_ALLOC);
}
void sched_mm_cid_exit_signals(struct task_struct *t)
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 5c2daa7ad3f90..8aa43204cb7dd 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -53,13 +53,24 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
enum task_work_notify_mode notify)
{
struct callback_head *head;
+ int flags = notify & TWA_FLAGS;
+ notify &= ~TWA_FLAGS;
if (notify == TWA_NMI_CURRENT) {
if (WARN_ON_ONCE(task != current))
return -EINVAL;
} else {
- /* record the work call stack in order to print it in KASAN reports */
- kasan_record_aux_stack(work);
+ /*
+ * Record the work call stack in order to print it in KASAN
+ * reports.
+ *
+ * Note that stack allocation can fail if TWAF_NO_ALLOC flag
+ * is set and new page is needed to expand the stack buffer.
+ */
+ if (flags & TWAF_NO_ALLOC)
+ kasan_record_aux_stack_noalloc(work);
+ else
+ kasan_record_aux_stack(work);
}
head = READ_ONCE(task->task_works);
