We can see following loop(10000 times) in trace_log:
[ 75.416137] ZL_DEBUG: reada_start_machine_dev:730: pid=771
comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.417413] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re =
ffff88003741e0c0, refcnt = 2 -> 1
[ 75.418611] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3
re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.419793] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re =
ffff88003741e0c0, refcnt = 2 -> 1
[ 75.421016] ZL_DEBUG: reada_start_machine_dev:730: pid=771
comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.422324] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re =
ffff88003741e0c0, refcnt = 2 -> 1
[ 75.423661] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3
re->ref_cnt ffff88003741e0c0 1 -> 2
[ 75.424882] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re =
ffff88003741e0c0, refcnt = 2 -> 1
...(10000 times)
[ 124.101672] ZL_DEBUG: reada_start_machine_dev:730: pid=771
comm=kworker/u2:3 re->ref_cnt ffff88003741e0c0 1 -> 2
[ 124.102850] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re =
ffff88003741e0c0, refcnt = 2 -> 1
[ 124.104008] ZL_DEBUG: __readahead_hook:129: pid=771 comm=kworker/u2:3
re->ref_cnt ffff88003741e0c0 1 -> 2
[ 124.105121] ZL_DEBUG: reada_extent_put:524: pid=771 comm=kworker/u2:3 re =
ffff88003741e0c0, refcnt = 2 -> 1
Reason:
If more than one user trigger reada in same extent, the first task
finished setting of reada data struct and call reada_start_machine()
to start, and the second task only add a ref_count but have not
add reada_extctl struct completely, the reada_extent can not finished
all jobs, and will be selected in __reada_start_machine() for 10000
times(total times in __reada_start_machine()).
Fix:
For a reada_extent without job, we don't need to run it, just return
0 to let caller break.
Signed-off-by: Zhao Lei <zhao...@cn.fujitsu.com>
---
fs/btrfs/reada.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index c65b42f..fb21bf0 100644
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -713,7 +713,7 @@ static int reada_start_machine_dev(struct btrfs_fs_info
*fs_info,
logical = re->logical;
spin_lock(&re->lock);
- if (re->scheduled_for == NULL) {
+ if (!re->scheduled_for && !list_empty(&re->extctl)) {
re->scheduled_for = dev;
need_kick = 1;
}
--
1.8.5.1
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