fs: sys_sync fix

s_syncing livelock avoidance was breaking data integrity guarantee of
sys_sync, by allowing sys_sync to skip writing or waiting for superblocks
if there is a concurrent sys_sync happening.

This livelock avoidance is much less important now that we don't have the
get_super_to_sync() call after every sb that we sync.  This was replaced
by __put_super_and_need_restart.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 1 insertions, 20 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index a9ee474f9691..e5eaa62fd17f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -652,18 +652,6 @@ void sync_inodes_sb(struct super_block *sb, int wait)
         sync_sb_inodes(sb, &wbc);
 }
 
-/*
- * Rather lame livelock avoidance.
- */
-static void set_sb_syncing(int val)
-{
-        struct super_block *sb;
-        spin_lock(&sb_lock);
-        list_for_each_entry_reverse(sb, &super_blocks, s_list)
-                sb->s_syncing = val;
-        spin_unlock(&sb_lock);
-}
-
 /**
  * sync_inodes - writes all inodes to disk
  * @wait: wait for completion
@@ -690,9 +678,6 @@ static void __sync_inodes(int wait)
         spin_lock(&sb_lock);
 restart:
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (sb->s_syncing)
-                        continue;
-                sb->s_syncing = 1;
                 sb->s_count++;
                 spin_unlock(&sb_lock);
                 down_read(&sb->s_umount);
@@ -710,13 +695,10 @@ restart:
 
 void sync_inodes(int wait)
 {
-        set_sb_syncing(0);
         __sync_inodes(0);
 
-        if (wait) {
-                set_sb_syncing(0);
+        if (wait)
                 __sync_inodes(1);
-        }
 }
 
 /**
diff --git a/include/linux/fs.h b/include/linux/fs.h
index fb59673c60b1..d7eba77f666e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1133,7 +1133,6 @@ struct super_block {
         struct rw_semaphore     s_umount;
         struct mutex            s_lock;
         int                     s_count;
-        int                     s_syncing;
         int                     s_need_sync_fs;
         atomic_t                s_active;
 #ifdef CONFIG_SECURITY