Re: [PATCH] padata: Always leave BHs disabled when running ->parallel()

[Herbert Xu]

On Wed, Nov 16, 2022 at 08:28:02PM -0500, Daniel Jordan wrote:
> A deadlock can happen when an overloaded system runs ->parallel() in the
> context of the current task:
> 
>     padata_do_parallel
>       ->parallel()
>         pcrypt_aead_enc/dec
>           padata_do_serial
>             spin_lock(&reorder->lock) // BHs still enabled
>               <interrupt>
>                 ...
>                   __do_softirq
>                     ...
>                       padata_do_serial
>                         spin_lock(&reorder->lock)
> 
> It's a bug for BHs to be on in _do_serial as Steffen points out, so
> ensure they're off in the "current task" case like they are in
> padata_parallel_worker to avoid this situation.
> 
> Reported-by: syzbot+bc05445bc14148d51915@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 4611ce224688 ("padata: allocate work structures for parallel jobs from a pool")
> Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> Acked-by: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
> ---
> 
> About the potential deadlock in padata_find_next(), I think this fix
> covers us there since that function is only called from
> padata_do_serial(), where BHs should now always be off, or
> invoke_padata_reorder(), where BHs are off as well.  The _bh spinlock
> variants in padata_reorder() seem redundant.
> 
>  kernel/padata.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt