From: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Marc Hartmayer reported:
[ 23.133876] Unable to handle kernel pointer dereference in virtual kernel address space
[ 23.133950] Failing address: 0000000000000000 TEID: 0000000000000483
[ 23.133954] Fault in home space mode while using kernel ASCE.
[ 23.133957] AS:000000001b8f0007 R3:0000000056cf4007 S:0000000056cf3800 P:000000000000003d
[ 23.134207] Oops: 0004 ilc:2 [#1] SMP
(snip)
[ 23.134516] Call Trace:
[ 23.134520] [<0000024e326caf28>] worker_thread+0x48/0x430
[ 23.134525] ([<0000024e326caf18>] worker_thread+0x38/0x430)
[ 23.134528] [<0000024e326d3a3e>] kthread+0x11e/0x130
[ 23.134533] [<0000024e3264b0dc>] __ret_from_fork+0x3c/0x60
[ 23.134536] [<0000024e333fb37a>] ret_from_fork+0xa/0x38
[ 23.134552] Last Breaking-Event-Address:
[ 23.134553] [<0000024e333f4c04>] mutex_unlock+0x24/0x30
[ 23.134562] Kernel panic - not syncing: Fatal exception: panic_on_oops
With debuging and analysis, worker_thread() accesses to the nullified
worker->pool when the newly created worker is destroyed before being
waken-up, in which case worker_thread() can see the result detach_worker()
reseting worker->pool to NULL at the begining.
Move the code "worker->pool = NULL;" out from detach_worker() to fix the
problem.
worker->pool had been designed to be constant for regular workers and
changeable for rescuer. To share attaching/detaching code for regular
and rescuer workers and to avoid worker->pool being accessed inadvertently
when the worker has been detached, worker->pool is reset to NULL when
detached no matter the worker is rescuer or not.
To maintain worker->pool being reset after detached, move the code
"worker->pool = NULL;" in the worker thread context after detached.
It is either be in the regular worker thread context after PF_WQ_WORKER
is cleared or in rescuer worker thread context with wq_pool_attach_mutex
held. So it is safe to do so.
Cc: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/87wmjj971b.fsf@xxxxxxxxxxxxx/
Reported-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>
Fixes: f4b7b53c94af ("workqueue: Detach workers directly in idle_cull_fn()")
Cc: stable@xxxxxxxxxxxxxxx # v6.11+
Signed-off-by: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
---
kernel/workqueue.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e7b005ff3750..6f2545037e57 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2709,7 +2709,6 @@ static void detach_worker(struct worker *worker)
unbind_worker(worker);
list_del(&worker->node);
- worker->pool = NULL;
}
/**
@@ -2729,6 +2728,7 @@ static void worker_detach_from_pool(struct worker *worker)
mutex_lock(&wq_pool_attach_mutex);
detach_worker(worker);
+ worker->pool = NULL;
mutex_unlock(&wq_pool_attach_mutex);
/* clear leftover flags without pool->lock after it is detached */
@@ -3349,7 +3349,11 @@ static int worker_thread(void *__worker)
if (unlikely(worker->flags & WORKER_DIE)) {
raw_spin_unlock_irq(&pool->lock);
set_pf_worker(false);
-
+ /*
+ * The worker is dead and PF_WQ_WORKER is cleared, worker->pool
+ * shouldn't be accessed, reset it to NULL in case otherwise.
+ */
+ worker->pool = NULL;
ida_free(&pool->worker_ida, worker->id);
return 0;
}
--
2.19.1.6.gb485710b
