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Subject[patch 40/40] fs: sys_sync fix
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Nick Piggin <npiggin@suse.de>

commit 856bf4d717feb8c55d4e2f817b71ebb70cfbc67b upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/fs-writeback.c | 20 +-------------------
include/linux/fs.h | 1 -
2 files changed, 1 insertion(+), 20 deletions(-)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -652,18 +652,6 @@ void sync_inodes_sb(struct super_block *
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);
- }
}

/**
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1080,7 +1080,6 @@ 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


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