This is a note to let you know that I've just added the patch titled padata: Always leave BHs disabled when running ->parallel() to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: padata-always-leave-bhs-disabled-when-running-parall.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 857f2cb25e7985bffab80634c31355b05c8ffbaa Author: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Date: Wed Nov 16 20:28:02 2022 -0500 padata: Always leave BHs disabled when running ->parallel() [ Upstream commit 34c3a47d20ae55b3600fed733bf96eafe9c500d5 ] 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> Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/padata.c b/kernel/padata.c index 18d3a5c699d8..9395b77fabb1 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;