On Mon, 31 Jan 2022 15:35:18 -0800
Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> Lockdep reports:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.16.0-rc1+ #142 Tainted: G OE
> ------------------------------------------------------
> cxl/1220 is trying to acquire lock:
> ffff979b85475460 (kn->active#144){++++}-{0:0}, at: __kernfs_remove+0x1ab/0x1e0
>
> but task is already holding lock:
> ffff979b87ab38e8 (&dev->lockdep_mutex#2/4){+.+.}-{3:3}, at: cxl_remove_ep+0x50c/0x5c0 [cxl_core]
>
> ...where cxl_remove_ep() is a helper that wants to delete ports while
> holding a lock on the host device for that port. That sets up a lockdep
> violation whereby target_list_show() can not rely holding the decoder's
> device lock while walking the target_list. Switch to a dedicated seqlock
> for this purpose.
>
> Reported-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
