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(-)
diff --git a/kernel/padata.c b/kernel/padata.c
index e5819bb8bd1d..97f51e0c1776 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -207,14 +207,16 @@ int padata_do_parallel(struct padata_shell *ps,
pw = padata_work_alloc();
spin_unlock(&padata_works_lock);
+ if (!pw) {
+ /* Maximum works limit exceeded, run in the current task. */
+ padata->parallel(padata);
+ }
+
rcu_read_unlock_bh();
if (pw) {
padata_work_init(pw, padata_parallel_worker, padata, 0);
queue_work(pinst->parallel_wq, &pw->pw_work);
- } else {
- /* Maximum works limit exceeded, run in the current task. */
- padata->parallel(padata);
}
return 0;
--
2.38.1
