[PATCH] padata: fix possible padata_works_lock deadlock

[PATCH] padata: fix possible padata_works_lock deadlock

[Daniel Jordan]

syzbot reports,

  WARNING: inconsistent lock state
  5.9.0-rc2-syzkaller #0 Not tainted
  --------------------------------
  inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
  syz-executor.0/26715 takes:
  (padata_works_lock){+.?.}-{2:2}, at: padata_do_parallel kernel/padata.c:220
  {IN-SOFTIRQ-W} state was registered at:
    spin_lock include/linux/spinlock.h:354 [inline]
    padata_do_parallel kernel/padata.c:220
    ...
    __do_softirq kernel/softirq.c:298
    ...
    sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1091
    asm_sysvec_apic_timer_interrupt arch/x86/include/asm/idtentry.h:581

   Possible unsafe locking scenario:

         CPU0
         ----
    lock(padata_works_lock);
    <Interrupt>
      lock(padata_works_lock);

padata_do_parallel() takes padata_works_lock with softirqs enabled, so a
deadlock is possible if, on the same CPU, the lock is acquired in
process context and then softirq handling done in an interrupt leads to
the same path.

Fix by leaving softirqs disabled while do_parallel holds
padata_works_lock.

Reported-by: syzbot+f4b9f49e38e25eb4ef52@syzkaller.appspotmail.com
Fixes: 4611ce2246889 ("padata: allocate work structures for parallel jobs from a pool")
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 kernel/padata.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 16cb894dc272..d4d3ba6e1728 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -215,12 +215,13 @@ int padata_do_parallel(struct padata_shell *ps,
 	padata->pd = pd;
 	padata->cb_cpu = *cb_cpu;
 
-	rcu_read_unlock_bh();
-
 	spin_lock(&padata_works_lock);
 	padata->seq_nr = ++pd->seq_nr;
 	pw = padata_work_alloc();
 	spin_unlock(&padata_works_lock);
+
+	rcu_read_unlock_bh();
+
 	if (pw) {
 		padata_work_init(pw, padata_parallel_worker, padata, 0);
 		queue_work(pinst->parallel_wq, &pw->pw_work);

base-commit: 9c7d619be5a002ea29c172df5e3c1227c22cbb41
-- 
2.28.0

Re: [PATCH] padata: fix possible padata_works_lock deadlock

[Herbert Xu]

On Wed, Sep 02, 2020 at 01:07:56PM -0400, Daniel Jordan wrote:
> syzbot reports,
> 
>   WARNING: inconsistent lock state
>   5.9.0-rc2-syzkaller #0 Not tainted
>   --------------------------------
>   inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
>   syz-executor.0/26715 takes:
>   (padata_works_lock){+.?.}-{2:2}, at: padata_do_parallel kernel/padata.c:220
>   {IN-SOFTIRQ-W} state was registered at:
>     spin_lock include/linux/spinlock.h:354 [inline]
>     padata_do_parallel kernel/padata.c:220
>     ...
>     __do_softirq kernel/softirq.c:298
>     ...
>     sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1091
>     asm_sysvec_apic_timer_interrupt arch/x86/include/asm/idtentry.h:581
> 
>    Possible unsafe locking scenario:
> 
>          CPU0
>          ----
>     lock(padata_works_lock);
>     <Interrupt>
>       lock(padata_works_lock);
> 
> padata_do_parallel() takes padata_works_lock with softirqs enabled, so a
> deadlock is possible if, on the same CPU, the lock is acquired in
> process context and then softirq handling done in an interrupt leads to
> the same path.
> 
> Fix by leaving softirqs disabled while do_parallel holds
> padata_works_lock.
> 
> Reported-by: syzbot+f4b9f49e38e25eb4ef52@syzkaller.appspotmail.com
> Fixes: 4611ce2246889 ("padata: allocate work structures for parallel jobs from a pool")
> Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: Steffen Klassert <steffen.klassert@secunet.com>
> Cc: linux-crypto@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  kernel/padata.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

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