On Tue, Apr 01, 2025 at 05:23:56PM +0530, Nilay Shroff wrote: > > > On 3/29/25 7:29 AM, Ming Lei wrote: > > On Fri, Mar 28, 2025 at 07:37:25AM -0700, syzbot wrote: > >> Hello, > >> > >> syzbot found the following issue on: > >> > >> HEAD commit: 1a9239bb4253 Merge tag 'net-next-6.15' of git://git.kernel.. > >> git tree: upstream > >> console output: https://syzkaller.appspot.com/x/log.txt?x=1384b43f980000 > >> kernel config: https://syzkaller.appspot.com/x/.config?x=c7163a109ac459a8 > >> dashboard link: https://syzkaller.appspot.com/bug?extid=4c7e0f9b94ad65811efb > >> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=178cfa4c580000 > >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11a8ca4c580000 > >> > >> Downloadable assets: > >> disk image: https://storage.googleapis.com/syzbot-assets/fc7dc9f0d9a7/disk-1a9239bb.raw.xz > >> vmlinux: https://storage.googleapis.com/syzbot-assets/f555a3ae03d3/vmlinux-1a9239bb.xz > >> kernel image: https://storage.googleapis.com/syzbot-assets/55f6ea74eaf2/bzImage-1a9239bb.xz > >> > >> IMPORTANT: if you fix the issue, please add the following tag to the commit: > >> Reported-by: syzbot+4c7e0f9b94ad65811efb@xxxxxxxxxxxxxxxxxxxxxxxxx > >> > > > > ... > > > >> > >> If you want syzbot to run the reproducer, reply with: > >> #syz test: git://repo/address.git branch-or-commit-hash > >> If you attach or paste a git patch, syzbot will apply it before testing. > > > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index ae8494d88897..d7a103dc258b 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -4465,14 +4465,12 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx( > > return NULL; > > } > > > > -static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, > > - struct request_queue *q) > > +static void __blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, > > + struct request_queue *q) > > { > > struct blk_mq_hw_ctx *hctx; > > unsigned long i, j; > > > > - /* protect against switching io scheduler */ > > - mutex_lock(&q->elevator_lock); > > for (i = 0; i < set->nr_hw_queues; i++) { > > int old_node; > > int node = blk_mq_get_hctx_node(set, i); > > @@ -4505,7 +4503,19 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, > > > > xa_for_each_start(&q->hctx_table, j, hctx, j) > > blk_mq_exit_hctx(q, set, hctx, j); > > - mutex_unlock(&q->elevator_lock); > > +} > > + > > +static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, > > + struct request_queue *q, bool lock) > > +{ > > + if (lock) { > > + /* protect against switching io scheduler */ > > + mutex_lock(&q->elevator_lock); > > + __blk_mq_realloc_hw_ctxs(set, q); > > + mutex_unlock(&q->elevator_lock); > > + } else { > > + __blk_mq_realloc_hw_ctxs(set, q); > > + } > > > > /* unregister cpuhp callbacks for exited hctxs */ > > blk_mq_remove_hw_queues_cpuhp(q); > > @@ -4537,7 +4547,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, > > > > xa_init(&q->hctx_table); > > > > - blk_mq_realloc_hw_ctxs(set, q); > > + blk_mq_realloc_hw_ctxs(set, q, false); > > if (!q->nr_hw_queues) > > goto err_hctxs; > > > > @@ -5033,7 +5043,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, > > fallback: > > blk_mq_update_queue_map(set); > > list_for_each_entry(q, &set->tag_list, tag_set_list) { > > - blk_mq_realloc_hw_ctxs(set, q); > > + blk_mq_realloc_hw_ctxs(set, q, true); > > > > if (q->nr_hw_queues != set->nr_hw_queues) { > > int i = prev_nr_hw_queues; > > > > This patch looks good to me, however after we fix this one, I found another splat. > I see that these new splats are side effect of commit ffa1e7ada456 ("block: Make > request_queue lockdep splats show up earlier"). > > IMO in the block layer code (unless it's in an IO submission path or a path where we > have already frozen queue) we may still want to allow memory allocation with GFP_KERNEL. > So in that sense, for example, we may acquire ->elevator_lock followed by fs_reclaim. If any memory GFP_KERNEL allocation grabs ->elevator_lock, it is one real deadlock risk. > Or in another words, shouldn't it be legitimate to acquire blk layer specific lock and > then allocate memory using GFP_KERNEL assuming we haven't freezed queue or we're not in > IO submission path. But this commit ffa1e7ada456 ("block: Make request_queue lockdep > splats show up earlier") now showing up some false-positive splat as well, please see > below: It depends if we may run GFP_KERNEL allocation with ->elevator_lock. I feel ->elevator_lock is still used too many... thanks, Ming
