padata: fix possible padata_works_lock deadlock

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
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/kernel/padata.c b/kernel/padata.c
index 16cb894dc272b13a5501ace7d512b7ccd6c44ed6..d4d3ba6e1728a2a00b5f30d53fbbfe0a8d07829e 100644 (file)
--- 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);