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| author | Al Viro <viro@zeniv.linux.org.uk> | 2010-08-09 12:05:43 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2010-08-09 16:49:01 -0400 |
| commit | 7a4dec53897ecd3367efb1e12fe8a4edc47dc0e9 (patch) | |
| tree | 31d4639522e1453a7f5c38aa2436ffdd6df5c60b /fs/super.c | |
| parent | 4f331f01b9c43bf001d3ffee578a97a1e0633eac (diff) | |
| download | lwn-7a4dec53897ecd3367efb1e12fe8a4edc47dc0e9.tar.gz lwn-7a4dec53897ecd3367efb1e12fe8a4edc47dc0e9.zip | |
Fix sget() race with failing mount
If sget() finds a matching superblock being set up, it'll
grab an active reference to it and grab s_umount. That's
fine - we'll wait for completion of foofs_get_sb() that way.
However, if said foofs_get_sb() fails we'll end up holding
the halfway-created superblock. deactivate_locked_super()
called by foofs_get_sb() will just unlock the sucker since
we are holding another active reference to it.
What we need is a way to tell if superblock has been successfully
set up. Unfortunately, neither ->s_root nor the check for
MS_ACTIVE quite fit. Cheap and easy way, suitable for backport:
new flag set by the (only) caller of ->get_sb(). If that flag
isn't present by the time sget() grabbed s_umount on preexisting
superblock it has found, it's seeing a stillborn and should
just bury it with deactivate_locked_super() (and repeat the search).
Longer term we want to set that flag in ->get_sb() instances (and
check for it to distinguish between "sget() found us a live sb"
and "sget() has allocated an sb, we need to set it up" in there,
instead of checking ->s_root as we do now).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Diffstat (limited to 'fs/super.c')
| -rw-r--r-- | fs/super.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/super.c b/fs/super.c index 3479ca6f005f..bd9eea4bb2bb 100644 --- a/fs/super.c +++ b/fs/super.c @@ -305,8 +305,13 @@ retry: if (s) { up_write(&s->s_umount); destroy_super(s); + s = NULL; } down_write(&old->s_umount); + if (unlikely(!(old->s_flags & MS_BORN))) { + deactivate_locked_super(old); + goto retry; + } return old; } } @@ -918,6 +923,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void goto out_free_secdata; BUG_ON(!mnt->mnt_sb); WARN_ON(!mnt->mnt_sb->s_bdi); + mnt->mnt_sb->s_flags |= MS_BORN; error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata); if (error) |