From 4fe7a0e13864238fe5b4cc2640e963581f96429e Mon Sep 17 00:00:00 2001 From: Zhao Lei Date: Tue, 26 Jan 2016 18:42:40 +0800 Subject: [PATCH] btrfs: reada: avoid undone reada extents in btrfs_reada_wait Reada background works is not designed to finish all jobs completely, it will break in following case: 1: When a device reaches workload limit (MAX_IN_FLIGHT) 2: Total reads reach max limit (10000) 3: All devices don't have queued more jobs, often happened in DUP case And if all background works exit with remaining jobs, btrfs_reada_wait() will wait indefinetelly. Above problem is rarely happened in old code, because: 1: Every work queues 2x new works So many works reduced chances of undone jobs. 2: One work will continue 10000 times loop in case of no-jobs It reduced no-thread window time. But after we fixed above case, the "undone reada extents" frequently happened. Fix: Check to ensure we have at least one thread if there are undone jobs in btrfs_reada_wait(). Signed-off-by: Zhao Lei Signed-off-by: David Sterba --- fs/btrfs/reada.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c index e97bc8e..5bcd567 100644 --- a/fs/btrfs/reada.c +++ b/fs/btrfs/reada.c @@ -953,8 +953,11 @@ struct reada_control *btrfs_reada_add(struct btrfs_root *root, int btrfs_reada_wait(void *handle) { struct reada_control *rc = handle; + struct btrfs_fs_info *fs_info = rc->root->fs_info; while (atomic_read(&rc->elems)) { + if (!atomic_read(&fs_info->reada_works_cnt)) + reada_start_machine(fs_info); wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0, 5 * HZ); dump_devs(rc->root->fs_info, @@ -971,9 +974,13 @@ int btrfs_reada_wait(void *handle) int btrfs_reada_wait(void *handle) { struct reada_control *rc = handle; + struct btrfs_fs_info *fs_info = rc->root->fs_info; while (atomic_read(&rc->elems)) { - wait_event(rc->wait, atomic_read(&rc->elems) == 0); + if (!atomic_read(&fs_info->reada_works_cnt)) + reada_start_machine(fs_info); + wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0, + (HZ + 9) / 10); } kref_put(&rc->refcnt, reada_control_release); -- 2.7.4