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writeback: Fix sync livelock due to b_dirty_time processing

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commit f9cae926f35e8230330f28c7b743ad088611a8de upstream.

When we are processing writeback for sync(2), move_expired_inodes()
didn't set any inode expiry value (older_than_this). This can result in
writeback never completing if there's steady stream of inodes added to
b_dirty_time list as writeback rechecks dirty lists after each writeback
round whether there's more work to be done. Fix the problem by using
sync(2) start time is inode expiry value when processing b_dirty_time
list similarly as for ordinarily dirtied inodes. This requires some
refactoring of older_than_this handling which simplifies the code
noticeably as a bonus.

Fixes: 0ae45f63d4 ("vfs: add support for a lazytime mount option")
CC: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jan Kara 2020-05-29 16:08:58 +02:00 • committed by Greg Kroah-Hartman
commit 6623c19042
2 changed files with 23 additions and 34 deletions
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13
include/trace/events/writeback.h
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@ -499,8 +499,9 @@ DEFINE_WBC_EVENT(wbc_writepage);
TRACE_EVENT(writeback_queue_io,
TP_PROTO(struct bdi_writeback *wb,
struct wb_writeback_work *work,
unsigned long dirtied_before,
int moved),
TP_ARGS(wb, work, moved),
TP_ARGS(wb, work, dirtied_before, moved),
TP_STRUCT__entry(
__array(char, name, 32)
__field(unsigned long, older)
@ -510,19 +511,17 @@ TRACE_EVENT(writeback_queue_io,
__field(unsigned int, cgroup_ino)
),
TP_fast_assign(
unsigned long *older_than_this = work->older_than_this;
strscpy_pad(__entry->name, bdi_dev_name(wb->bdi), 32);
__entry->older = older_than_this ? *older_than_this : 0;
__entry->age = older_than_this ?
(jiffies - *older_than_this) * 1000 / HZ : -1;
__entry->older = dirtied_before;
__entry->age = (jiffies - dirtied_before) * 1000 / HZ;
__entry->moved = moved;
__entry->reason = work->reason;
__entry->cgroup_ino = __trace_wb_assign_cgroup(wb);
),
TP_printk("bdi %s: older=%lu age=%ld enqueue=%d reason=%s cgroup_ino=%u",
__entry->name,
__entry->older, /* older_than_this in jiffies */
__entry->age, /* older_than_this in relative milliseconds */
__entry->older, /* dirtied_before in jiffies */
__entry->age, /* dirtied_before in relative milliseconds */
__entry->moved,
__print_symbolic(__entry->reason, WB_WORK_REASON),
__entry->cgroup_ino