Skip to content

Commit

Permalink
writeback: Fix sync livelock due to b_dirty_time processing
Browse files Browse the repository at this point in the history 
commit f9cae92 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: 0ae45f6 ("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>
  • Loading branch information
@jankara @gregkh
jankara authored and gregkh committed Sep 3, 2020
1 parent d74c235 commit 05ae7cf
Show file tree
Hide file tree
Showing 2 changed files with 23 additions and 34 deletions.
44 changes: 17 additions & 27 deletions fs/fs-writeback.c
View file
Expand Up @@ -42,7 +42,6 @@
struct wb_writeback_work {
long nr_pages;
struct super_block *sb;
unsigned long *older_than_this;
enum writeback_sync_modes sync_mode;
unsigned int tagged_writepages:1;
unsigned int for_kupdate:1;
Expand Down Expand Up @@ -1234,33 +1233,23 @@ static bool inode_dirtied_after(struct inode *inode, unsigned long t)
#define EXPIRE_DIRTY_ATIME 0x0001

/*
* Move expired (dirtied before work->older_than_this) dirty inodes from
* Move expired (dirtied before dirtied_before) dirty inodes from
* @delaying_queue to @dispatch_queue.
*/
static int move_expired_inodes(struct list_head *delaying_queue,
struct list_head *dispatch_queue,
int flags,
struct wb_writeback_work *work)
int flags, unsigned long dirtied_before)
{
unsigned long *older_than_this = NULL;
unsigned long expire_time;
LIST_HEAD(tmp);
struct list_head *pos, *node;
struct super_block *sb = NULL;
struct inode *inode;
int do_sb_sort = 0;
int moved = 0;

if ((flags & EXPIRE_DIRTY_ATIME) == 0)
older_than_this = work->older_than_this;
else if (!work->for_sync) {
expire_time = jiffies - (dirtytime_expire_interval * HZ);
older_than_this = &expire_time;
}
while (!list_empty(delaying_queue)) {
inode = wb_inode(delaying_queue->prev);
if (older_than_this &&
inode_dirtied_after(inode, *older_than_this))
if (inode_dirtied_after(inode, dirtied_before))
break;
list_move(&inode->i_io_list, &tmp);
moved++;
Expand Down Expand Up @@ -1306,18 +1295,22 @@ static int move_expired_inodes(struct list_head *delaying_queue,
* |
* +--> dequeue for IO
*/
static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
unsigned long dirtied_before)
{
int moved;
unsigned long time_expire_jif = dirtied_before;

assert_spin_locked(&wb->list_lock);
list_splice_init(&wb->b_more_io, &wb->b_io);
moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, 0, work);
moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, 0, dirtied_before);
if (!work->for_sync)
time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
EXPIRE_DIRTY_ATIME, work);
EXPIRE_DIRTY_ATIME, time_expire_jif);
if (moved)
wb_io_lists_populated(wb);
trace_writeback_queue_io(wb, work, moved);
trace_writeback_queue_io(wb, work, dirtied_before, moved);
}

static int write_inode(struct inode *inode, struct writeback_control *wbc)
Expand Down Expand Up @@ -1829,7 +1822,7 @@ static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
blk_start_plug(&plug);
spin_lock(&wb->list_lock);
if (list_empty(&wb->b_io))
queue_io(wb, &work);
queue_io(wb, &work, jiffies);
__writeback_inodes_wb(wb, &work);
spin_unlock(&wb->list_lock);
blk_finish_plug(&plug);
Expand All @@ -1849,22 +1842,19 @@ static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
* takes longer than a dirty_writeback_interval interval, then leave a
* one-second gap.
*
* older_than_this takes precedence over nr_to_write. So we'll only write back
* dirtied_before takes precedence over nr_to_write. So we'll only write back
* all dirty pages if they are all attached to "old" mappings.
*/
static long wb_writeback(struct bdi_writeback *wb,
struct wb_writeback_work *work)
{
unsigned long wb_start = jiffies;
long nr_pages = work->nr_pages;
unsigned long oldest_jif;
unsigned long dirtied_before = jiffies;
struct inode *inode;
long progress;
struct blk_plug plug;

oldest_jif = jiffies;
work->older_than_this = &oldest_jif;

blk_start_plug(&plug);
spin_lock(&wb->list_lock);
for (;;) {
Expand Down Expand Up @@ -1898,14 +1888,14 @@ static long wb_writeback(struct bdi_writeback *wb,
* safe.
*/
if (work->for_kupdate) {
oldest_jif = jiffies -
dirtied_before = jiffies -
msecs_to_jiffies(dirty_expire_interval * 10);
} else if (work->for_background)
oldest_jif = jiffies;
dirtied_before = jiffies;

trace_writeback_start(wb, work);
if (list_empty(&wb->b_io))
queue_io(wb, work);
queue_io(wb, work, dirtied_before);
if (work->sb)
progress = writeback_sb_inodes(work->sb, wb, work);
else
Expand Down
13 changes: 6 additions & 7 deletions include/trace/events/writeback.h
View file
Expand Up @@ -498,8 +498,9 @@ 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)
Expand All @@ -509,19 +510,17 @@ TRACE_EVENT(writeback_queue_io,
__field(ino_t, 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=%lu",
__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),
(unsigned long)__entry->cgroup_ino
Expand Down

0 comments on commit 05ae7cf

Please sign in to comment.