diff options
| author | Miklos Szeredi | 2011-11-21 12:11:31 +0100 |
|---|---|---|
| committer | Al Viro | 2012-01-06 23:20:12 -0500 |
| commit | 4ed5e82fe77f4147cf386327c9a63a2dd7eff518 (patch) | |
| tree | f4eaeefaf5d293014457892ac31f878eece07331 /include/linux | |
| parent | 39f7c4db1d2d9e2e2a90abdf34811783089d217d (diff) | |
vfs: protect remounting superblock read-only
Currently remouting superblock read-only is racy in a major way.
With the per mount read-only infrastructure it is now possible to
prevent most races, which this patch attempts.
Before starting the remount read-only, iterate through all mounts
belonging to the superblock and if none of them have any pending
writes, set sb->s_readonly_remount. This indicates that remount is in
progress and no further write requests are allowed. If the remount
succeeds set MS_RDONLY and reset s_readonly_remount.
If the remounting is unsuccessful just reset s_readonly_remount.
This can result in transient EROFS errors, despite the fact the
remount failed. Unfortunately hodling off writes is difficult as
remount itself may touch the filesystem (e.g. through load_nls())
which would deadlock.
A later patch deals with delayed writes due to nlink going to zero.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/fs.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h index 03385acd71e8..7b8a681b1ef4 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1482,6 +1482,9 @@ struct super_block { int cleancache_poolid; struct shrinker s_shrink; /* per-sb shrinker handle */ + + /* Being remounted read-only */ + int s_readonly_remount; }; /* superblock cache pruning functions */ |