From 20b2e3029eef277cd93a46a991004260057e1a9e Mon Sep 17 00:00:00 2001 From: Zhao Lei Date: Thu, 4 Jun 2015 20:09:15 +0800 Subject: btrfs: Fix lockdep warning of wr_ctx->wr_lock in scrub_free_wr_ctx() lockdep report following warning in test: [25176.843958] ================================= [25176.844519] [ INFO: inconsistent lock state ] [25176.845047] 4.1.0-rc3 #22 Tainted: G W [25176.845591] --------------------------------- [25176.846153] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. [25176.846713] fsstress/26661 [HC0[0]:SC1[1]:HE1:SE0] takes: [25176.847246] (&wr_ctx->wr_lock){+.?...}, at: [] scrub_free_ctx+0x2d/0xf0 [btrfs] [25176.847838] {SOFTIRQ-ON-W} state was registered at: [25176.848396] [] __lock_acquire+0x6a0/0xe10 [25176.848955] [] lock_acquire+0xce/0x2c0 [25176.849491] [] mutex_lock_nested+0x7f/0x410 [25176.850029] [] scrub_stripe+0x4df/0x1080 [btrfs] [25176.850575] [] scrub_chunk.isra.19+0x111/0x130 [btrfs] [25176.851110] [] scrub_enumerate_chunks+0x27c/0x510 [btrfs] [25176.851660] [] btrfs_scrub_dev+0x1c7/0x6c0 [btrfs] [25176.852189] [] btrfs_dev_replace_start+0x36e/0x450 [btrfs] [25176.852771] [] btrfs_ioctl+0x1e10/0x2d20 [btrfs] [25176.853315] [] do_vfs_ioctl+0x318/0x570 [25176.853868] [] SyS_ioctl+0x41/0x80 [25176.854406] [] system_call_fastpath+0x12/0x6f [25176.854935] irq event stamp: 51506 [25176.855511] hardirqs last enabled at (51506): [] vprintk_emit+0x225/0x5e0 [25176.856059] hardirqs last disabled at (51505): [] vprintk_emit+0xb7/0x5e0 [25176.856642] softirqs last enabled at (50886): [] __do_softirq+0x363/0x640 [25176.857184] softirqs last disabled at (50949): [] irq_exit+0x10d/0x120 [25176.857746] other info that might help us debug this: [25176.858845] Possible unsafe locking scenario: [25176.859981] CPU0 [25176.860537] ---- [25176.861059] lock(&wr_ctx->wr_lock); [25176.861705] [25176.862272] lock(&wr_ctx->wr_lock); [25176.862881] *** DEADLOCK *** Reason: Above warning is caused by: Interrupt -> bio_endio() -> ... -> scrub_put_ctx() -> scrub_free_ctx() *1 -> ... -> mutex_lock(&wr_ctx->wr_lock); scrub_put_ctx() is allowed to be called in end_bio interrupt, but in code design, it will never call scrub_free_ctx(sctx) in interrupe context(above *1), because btrfs_scrub_dev() get one additional reference of sctx->refs, which makes scrub_free_ctx() only called withine btrfs_scrub_dev(). Now the code runs out of our wish, because free sequence in scrub_pending_bio_dec() have a gap. Current code: -----------------------------------+----------------------------------- scrub_pending_bio_dec() | btrfs_scrub_dev -----------------------------------+----------------------------------- atomic_dec(&sctx->bios_in_flight); | wake_up(&sctx->list_wait); | | scrub_put_ctx() | -> atomic_dec_and_test(&sctx->refs) scrub_put_ctx(sctx); | -> atomic_dec_and_test(&sctx->refs)| -> scrub_free_ctx() | -----------------------------------+----------------------------------- We expected: -----------------------------------+----------------------------------- scrub_pending_bio_dec() | btrfs_scrub_dev -----------------------------------+----------------------------------- atomic_dec(&sctx->bios_in_flight); | wake_up(&sctx->list_wait); | scrub_put_ctx(sctx); | -> atomic_dec_and_test(&sctx->refs)| | scrub_put_ctx() | -> atomic_dec_and_test(&sctx->refs) | -> scrub_free_ctx() -----------------------------------+----------------------------------- Fix: Move scrub_pending_bio_dec() to a workqueue, to avoid this function run in interrupt context. Tested by check tracelog in debug. Changelog v1->v2: Use workqueue instead of adjust function call sequence in v1, because v1 will introduce a bug pointed out by: Filipe David Manana Reported-by: Qu Wenruo Signed-off-by: Zhao Lei Reviewed-by: Filipe Manana Signed-off-by: Chris Mason --- fs/btrfs/async-thread.c | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/btrfs/async-thread.c') diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c index df9932b00d08..1ce06c849a86 100644 --- a/fs/btrfs/async-thread.c +++ b/fs/btrfs/async-thread.c @@ -85,6 +85,7 @@ BTRFS_WORK_HELPER(extent_refs_helper); BTRFS_WORK_HELPER(scrub_helper); BTRFS_WORK_HELPER(scrubwrc_helper); BTRFS_WORK_HELPER(scrubnc_helper); +BTRFS_WORK_HELPER(scrubparity_helper); static struct __btrfs_workqueue * __btrfs_alloc_workqueue(const char *name, unsigned int flags, int max_active, -- cgit v1.2.3