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, which only triggers on unmount.
---
Index: linux-2.6/fs/fs-writeback.c
===================================================================
--- linux-2.6.orig/fs/fs-writeback.c
+++ linux-2.6/fs/fs-writeback.c
@@ -645,18 +645,6 @@ 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
@@ -683,9 +671,6 @@ 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);
@@ -703,13 +688,10 @@ restart:
void sync_inodes(int wait)
{
- set_sb_syncing(0);
__sync_inodes(0);
- if (wait) {
- set_sb_syncing(0);
+ if (wait)
__sync_inodes(1);
- }
}
/**
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -1122,7 +1122,6 @@ 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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