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| author |   Miklos Szeredi <mszeredi@suse.cz> | 2011-11-21 12:11:31 +0100 |
|---|---|---|
| committer |   Al Viro <viro@zeniv.linux.org.uk> | 2012-01-06 23:20:12 -0500 |
| commit | 4ed5e82fe77f4147cf386327c9a63a2dd7eff518 (patch) | |
| tree | f4eaeefaf5d293014457892ac31f878eece07331 /fs/internal.h | |
| parent | vfs: keep list of mounts for each superblock (diff) | |
| download | linux-dev-4ed5e82fe77f4147cf386327c9a63a2dd7eff518.tar.xz linux-dev-4ed5e82fe77f4147cf386327c9a63a2dd7eff518.zip | |
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 'fs/internal.h')
| -rw-r--r-- | fs/internal.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/internal.h b/fs/internal.h index 2523a4029452..9962c59ba280 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -52,6 +52,7 @@ extern int finish_automount(struct vfsmount *, struct path *); extern void mnt_make_longterm(struct vfsmount *); extern void mnt_make_shortterm(struct vfsmount *); +extern int sb_prepare_remount_readonly(struct super_block *); extern void __init mnt_init(void); |