On Thu, Sep 12, 2024 at 11:23 AM +0800, Lai Jiangshan jiangshanlai@gmail.com wrote:
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
[…snip…]
Hi, Lai,
so I tested several things:
1. f4b7b53c94af ("workqueue: Detach workers directly in idle_cull_fn()") is the commit that introduced the bug 2. with your fix applied I cannot reproduce the bug
Therefore
Tested-by: Marc Hartmayer mhartmay@linux.ibm.com
Thanks for the quick fix!
--- Kind regards / Beste Grüße Marc Hartmayer
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