From: Lai Jiangshan jiangshan.ljs@antgroup.com

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@linux.ibm.com Link: https://lore.kernel.org/lkml/87wmjj971b.fsf@linux.ibm.com/ Reported-by: Marc Hartmayer mhartmay@linux.ibm.com Fixes: f4b7b53c94af ("workqueue: Detach workers directly in idle_cull_fn()") Cc: stable@vger.kernel.org # v6.11+ Signed-off-by: Lai Jiangshan jiangshan.ljs@antgroup.com --- 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; }