| Date | Wed, 28 Sep 2011 15:02:05 -0700 | From | Greg KH <> | Subject | [161/244] writeback: update dirtied_when for synced inode to prevent livelock |
| |
3.0-stable review patch. If anyone has any objections, please let us know.
------------------
From: Wu Fengguang <fengguang.wu@intel.com>
commit 94c3dcbb0b0cdfd82cedd21705424d8044edc42c upstream.
Explicitly update .dirtied_when on synced inodes, so that they are no longer considered for writeback in the next round.
It can prevent both of the following livelock schemes:
- while true; do echo data >> f; done - while true; do touch f; done (in theory)
The exact livelock condition is, during sync(1):
(1) no new inodes are dirtied (2) an inode being actively dirtied
On (2), the inode will be tagged and synced with .nr_to_write=LONG_MAX. When finished, it will be redirty_tail()ed because it's still dirty and (.nr_to_write > 0). redirty_tail() won't update its ->dirtied_when on condition (1). The sync work will then revisit it on the next queue_io() and find it eligible again because its old ->dirtied_when predates the sync work start time.
We'll do more aggressive "keep writeback as long as we wrote something" logic in wb_writeback(). The "use LONG_MAX .nr_to_write" trick in commit b9543dac5bbc ("writeback: avoid livelocking WB_SYNC_ALL writeback") will no longer be enough to stop sync livelock.
Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- fs/fs-writeback.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -419,6 +419,15 @@ writeback_single_inode(struct inode *ino spin_lock(&inode->i_lock); inode->i_state &= ~I_SYNC; if (!(inode->i_state & I_FREEING)) { + /* + * Sync livelock prevention. Each inode is tagged and synced in + * one shot. If still dirty, it will be redirty_tail()'ed below. + * Update the dirty time to prevent enqueue and sync it again. + */ + if ((inode->i_state & I_DIRTY) && + (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)) + inode->dirtied_when = jiffies; + if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) { /* * We didn't write back all the pages. nfs_writepages()
|