The sync() is performed in two stages: the WB_SYNC_NONE sync and the WB_SYNC_ALL sync. It is necessary to tag both stages with wbc.for_sync, so as to prevent either of them being livelocked. The basic livelock scheme will be based on the sync_after timestamp. Inodes dirtied after that won't be queued for IO. The timestamp could be recorded as early as the sync() time, this patch lazily sets it in writeback_inodes_sb()/sync_inodes_sb(). This will stop livelock, but may do more work than necessary. Note that writeback_inodes_sb() is called by not only sync(), they are treated the same because the other callers need the same livelock prevention. CC: Jan Kara Signed-off-by: Wu Fengguang --- fs/fs-writeback.c | 21 ++++++++++++--------- include/linux/writeback.h | 1 + 2 files changed, 13 insertions(+), 9 deletions(-) --- linux-next.orig/fs/fs-writeback.c 2010-07-28 17:05:17.000000000 +0800 +++ linux-next/fs/fs-writeback.c 2010-07-28 21:21:31.000000000 +0800 @@ -36,6 +36,8 @@ struct wb_writeback_work { long nr_pages; struct super_block *sb; enum writeback_sync_modes sync_mode; + unsigned long sync_after; + unsigned int for_sync:1; unsigned int for_kupdate:1; unsigned int range_cyclic:1; unsigned int for_background:1; @@ -1086,20 +1090,17 @@ static void wait_sb_inodes(struct super_ */ void writeback_inodes_sb(struct super_block *sb) { - unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY); - unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS); DECLARE_COMPLETION_ONSTACK(done); struct wb_writeback_work work = { .sb = sb, .sync_mode = WB_SYNC_NONE, + .for_sync = 1, + .sync_after = jiffies, .done = &done, }; WARN_ON(!rwsem_is_locked(&sb->s_umount)); - work.nr_pages = nr_dirty + nr_unstable + - (inodes_stat.nr_inodes - inodes_stat.nr_unused); - bdi_queue_work(sb->s_bdi, &work); wait_for_completion(&done); } @@ -1137,6 +1138,8 @@ void sync_inodes_sb(struct super_block * struct wb_writeback_work work = { .sb = sb, .sync_mode = WB_SYNC_ALL, + .for_sync = 1, + .sync_after = jiffies, .nr_pages = LONG_MAX, .range_cyclic = 0, .done = &done, --- linux-next.orig/include/linux/writeback.h 2010-07-28 17:05:17.000000000 +0800 +++ linux-next/include/linux/writeback.h 2010-07-28 21:24:54.000000000 +0800 @@ -48,6 +48,7 @@ struct writeback_control { unsigned encountered_congestion:1; /* An output: a queue is full */ unsigned for_kupdate:1; /* A kupdate writeback */ unsigned for_background:1; /* A background writeback */ + unsigned for_sync:1; /* A writeback for sync */ unsigned for_reclaim:1; /* Invoked from the page allocator */ unsigned range_cyclic:1; /* range_start is cyclic */ }; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/