redonkable
/
alistair23-linux
1
0
Fork 0
Code Releases Activity

btrfs: fix racy access to discard_ctl data 

Because only one discard worker may be running at any given point, it
could have been safe to modify ->prev_discard, etc. without
synchronization, if not for @override flag in
btrfs_discard_schedule_work() and delayed_work_pending() returning false
while workfn is running.

That may lead to torn reads of u64 for some architectures, but that's
not a big problem as only slightly affects the discard rate.

Suggested-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
zero-sugar-mainline-defconfig
Pavel Begunkov 2020-12-06 15:56:21 +00:00 committed by David Sterba
parent ea9ed87c73
commit 1ea2872fc6
1 changed files with 3 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
fs/btrfs/discard.c
View File

@ -477,13 +477,6 @@ static void btrfs_discard_workfn(struct work_struct *work)
discard_ctl->discard_extent_bytes += trimmed;
}
/*
* Updated without locks as this is inside the workfn and nothing else
* is reading the values
*/
discard_ctl->prev_discard = trimmed;
discard_ctl->prev_discard_time = ktime_get_ns();
/* Determine next steps for a block_group */
if (block_group->discard_cursor >= btrfs_block_group_end(block_group)) {
if (discard_state == BTRFS_DISCARD_BITMAPS) {
@ -499,7 +492,10 @@ static void btrfs_discard_workfn(struct work_struct *work)
}
}
now = ktime_get_ns();
spin_lock(&discard_ctl->lock);
discard_ctl->prev_discard = trimmed;
discard_ctl->prev_discard_time = now;
discard_ctl->block_group = NULL;
spin_unlock(&discard_ctl->lock);