Re: lockdep deadlock warning

[Vincent Whitchurch <vincent.whitchurch@axis.com>]

On Mon, May 23, 2022 at 02:38:02PM +0200, Vincent Whitchurch wrote:
> On Mon, Feb 14, 2022 at 10:19:30PM +0530, Shyam Prasad N wrote:
> > It's about a circular dependency locking fs_reclaim lock with srv_mutex held.
> > Does someone here understand this dependency?
> 
> The crypto shash allocation does allocations with GFP_KERNEL (i.e.,
> GFP_NOFS is not set and so fs reclaim can be triggered) and this is
> called under the CIFS srv_mutex.  However, the CIFS srv_mutex is also
> used in the reclaim path as the splat shows.  This is the dependency
> which lockdep is complaining about.
> 
> A way to remove this particular dependency is to make CIFS do a
> memalloc_nofs_save/restore() around the places it takes the srv_mutex.
> However, doing this does not solve the lockdep splats completely since
> there is another dependency via some internal locks in crypto, see the
> log below.

I have now sent out a patch to use memalloc_nofs_*.  There are other
GFP_KERNEL allocations in CIFS done under the srv_mutex (such as the one
in SMB2_sess_auth_rawntlmssp_negotiate()) besides the shash allocations,
so that patch is needed even if something is done later to move the
crypto shash allocations out of that mutex.

 https://lore.kernel.org/linux-cifs/20220530132155.4019006-1-vincent.whitchurch@axis.com/