Messages in this thread | | | Date | Wed, 30 Oct 2019 10:02:46 -0700 | From | Eric Biggers <> | Subject | Re: [PATCH 2/2] f2fs: support data compression |
| |
On Wed, Oct 30, 2019 at 04:43:52PM +0800, Chao Yu wrote: > >>>> static void bio_post_read_processing(struct bio_post_read_ctx *ctx) > >>>> { > >>>> - /* > >>>> - * We use different work queues for decryption and for verity because > >>>> - * verity may require reading metadata pages that need decryption, and > >>>> - * we shouldn't recurse to the same workqueue. > >>>> - */ > >>> > >>> Why is it okay (i.e., no deadlocks) to no longer use different work queues for > >>> decryption and for verity? See the comment above which is being deleted. > >> > >> Could you explain more about how deadlock happen? or share me a link address if > >> you have described that case somewhere? > >> > > > > The verity work can read pages from the file which require decryption. I'm > > concerned that it could deadlock if the work is scheduled on the same workqueue. > > I assume you've tried one workqueue, and suffered deadlock.. > > > Granted, I'm not an expert in Linux workqueues, so if you've investigated this > > and determined that it's safe, can you explain why? > > I'm not familiar with workqueue... I guess it may not safe that if the work is > scheduled to the same cpu in where verity was waiting for data? if the work is > scheduled to other cpu, it may be safe. > > I can check that before splitting the workqueue for verity and decrypt/decompress. >
Yes this is a real problem, try 'kvm-xfstests -c f2fs/encrypt generic/579'. The worker thread gets deadlocked in f2fs_read_merkle_tree_page() waiting for the Merkle tree page to be decrypted. This is with the v2 compression patch; it works fine on current mainline.
INFO: task kworker/u5:0:61 blocked for more than 30 seconds. Not tainted 5.4.0-rc1-00119-g464e31ba60d0 #13 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kworker/u5:0 D 0 61 2 0x80004000 Workqueue: f2fs_post_read_wq f2fs_post_read_work Call Trace: context_switch kernel/sched/core.c:3384 [inline] __schedule+0x299/0x6c0 kernel/sched/core.c:4069 schedule+0x44/0xd0 kernel/sched/core.c:4136 io_schedule+0x11/0x40 kernel/sched/core.c:5780 wait_on_page_bit_common mm/filemap.c:1174 [inline] wait_on_page_bit mm/filemap.c:1223 [inline] wait_on_page_locked include/linux/pagemap.h:527 [inline] wait_on_page_locked include/linux/pagemap.h:524 [inline] wait_on_page_read mm/filemap.c:2767 [inline] do_read_cache_page+0x407/0x660 mm/filemap.c:2810 read_cache_page+0xd/0x10 mm/filemap.c:2894 f2fs_read_merkle_tree_page+0x2e/0x30 include/linux/pagemap.h:396 verify_page+0x110/0x560 fs/verity/verify.c:120 fsverity_verify_bio+0xe6/0x1a0 fs/verity/verify.c:239 verity_work fs/f2fs/data.c:142 [inline] f2fs_post_read_work+0x36/0x50 fs/f2fs/data.c:160 process_one_work+0x225/0x550 kernel/workqueue.c:2269 worker_thread+0x4b/0x3c0 kernel/workqueue.c:2415 kthread+0x125/0x140 kernel/kthread.c:255 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352 INFO: task kworker/u5:1:1140 blocked for more than 30 seconds. Not tainted 5.4.0-rc1-00119-g464e31ba60d0 #13 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kworker/u5:1 D 0 1140 2 0x80004000 Workqueue: f2fs_post_read_wq f2fs_post_read_work Call Trace: context_switch kernel/sched/core.c:3384 [inline] __schedule+0x299/0x6c0 kernel/sched/core.c:4069 schedule+0x44/0xd0 kernel/sched/core.c:4136 io_schedule+0x11/0x40 kernel/sched/core.c:5780 wait_on_page_bit_common mm/filemap.c:1174 [inline] wait_on_page_bit mm/filemap.c:1223 [inline] wait_on_page_locked include/linux/pagemap.h:527 [inline] wait_on_page_locked include/linux/pagemap.h:524 [inline] wait_on_page_read mm/filemap.c:2767 [inline] do_read_cache_page+0x407/0x660 mm/filemap.c:2810 read_cache_page+0xd/0x10 mm/filemap.c:2894 f2fs_read_merkle_tree_page+0x2e/0x30 include/linux/pagemap.h:396 verify_page+0x110/0x560 fs/verity/verify.c:120 fsverity_verify_bio+0xe6/0x1a0 fs/verity/verify.c:239 verity_work fs/f2fs/data.c:142 [inline] f2fs_post_read_work+0x36/0x50 fs/f2fs/data.c:160 process_one_work+0x225/0x550 kernel/workqueue.c:2269 worker_thread+0x4b/0x3c0 kernel/workqueue.c:2415 kthread+0x125/0x140 kernel/kthread.c:255 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Showing all locks held in the system: 1 lock held by khungtaskd/21: #0: ffffffff82250520 (rcu_read_lock){....}, at: rcu_lock_acquire.constprop.0+0x0/0x30 include/trace/events/lock.h:13 2 locks held by kworker/u5:0/61: #0: ffff88807b78eb28 ((wq_completion)f2fs_post_read_wq){+.+.}, at: set_work_data kernel/workqueue.c:619 [inline] #0: ffff88807b78eb28 ((wq_completion)f2fs_post_read_wq){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline] #0: ffff88807b78eb28 ((wq_completion)f2fs_post_read_wq){+.+.}, at: process_one_work+0x1ad/0x550 kernel/workqueue.c:2240 #1: ffffc90000253e50 ((work_completion)(&ctx->work)){+.+.}, at: set_work_data kernel/workqueue.c:619 [inline] #1: ffffc90000253e50 ((work_completion)(&ctx->work)){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline] #1: ffffc90000253e50 ((work_completion)(&ctx->work)){+.+.}, at: process_one_work+0x1ad/0x550 kernel/workqueue.c:2240 2 locks held by kworker/u5:1/1140: #0: ffff88807b78eb28 ((wq_completion)f2fs_post_read_wq){+.+.}, at: set_work_data kernel/workqueue.c:619 [inline] #0: ffff88807b78eb28 ((wq_completion)f2fs_post_read_wq){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline] #0: ffff88807b78eb28 ((wq_completion)f2fs_post_read_wq){+.+.}, at: process_one_work+0x1ad/0x550 kernel/workqueue.c:2240 #1: ffffc9000174be50 ((work_completion)(&ctx->work)){+.+.}, at: set_work_data kernel/workqueue.c:619 [inline] #1: ffffc9000174be50 ((work_completion)(&ctx->work)){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:647 [inline] #1: ffffc9000174be50 ((work_completion)(&ctx->work)){+.+.}, at: process_one_work+0x1ad/0x550 kernel/workqueue.c:2240
| |