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fs/super.c: sync ro remount after blocking writers

Move sync_filesystem() after sb_prepare_remount_readonly().  If writers
sneak in anywhere from sync_filesystem() to sb_prepare_remount_readonly()
it can cause inodes to be dirtied and writeback to occur well after
sys_mount() has completely successfully.

This was spotted by corrupted ubifs filesystems on reboot, but appears
that it can cause issues with any filesystem using writeback.

Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
CC: Richard Weinberger <richard@nod.at>
Co-authored-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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1 parent 9115eac commit 807612db2f9940b9fa6deaef054eb16d51bd3e00 @aeruder aeruder committed with Al Viro Jan 30, 2014
Showing with 2 additions and 1 deletion.
  1. +2 −1 fs/super.c
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@@ -703,7 +703,6 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
if (flags & MS_RDONLY)
acct_auto_close(sb);
shrink_dcache_sb(sb);
- sync_filesystem(sb);
remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
@@ -720,6 +719,8 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
}
}
+ sync_filesystem(sb);
+
if (sb->s_op->remount_fs) {
retval = sb->s_op->remount_fs(sb, &flags, data);
if (retval) {

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