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Subject[PATCH] writeback_inodes can race with unmount
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Date
There's a small window where the filesystem can be unmounted during
writeback_inodes. The end result is the iput done by sync_sb_inodes
could be done after the FS put_super and and the super has been removed
from all lists.

The fix is to hold the s_umount sem during sync_sb_inodes to make sure
the FS doesn't get unmounted.

Index: linux.t/fs/fs-writeback.c
===================================================================
--- linux.t.orig/fs/fs-writeback.c 2004-06-08 14:45:49.000000000 -0400
+++ linux.t/fs/fs-writeback.c 2004-06-08 14:47:58.000000000 -0400
@@ -360,9 +360,18 @@ restart:
sb = sb_entry(super_blocks.prev);
for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
if (!list_empty(&sb->s_dirty) || !list_empty(&sb->s_io)) {
+ /* we're making our own get_super here */
sb->s_count++;
spin_unlock(&sb_lock);
- sync_sb_inodes(sb, wbc);
+ /* if we can't get the readlock, there's no sense in
+ * waiting around, most of the time the FS is going
+ * to be unmounted by the time it is released
+ */
+ if (down_read_trylock(&sb->s_umount)) {
+ if (sb->s_root)
+ sync_sb_inodes(sb, wbc);
+ up_read(&sb->s_umount);
+ }
spin_lock(&sb_lock);
if (__put_super(sb))
goto restart;

-
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