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authorAl Viro <viro@zeniv.linux.org.uk>2010-08-09 12:05:43 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2010-08-09 16:49:01 -0400
commit7a4dec53897ecd3367efb1e12fe8a4edc47dc0e9 (patch)
tree31d4639522e1453a7f5c38aa2436ffdd6df5c60b /fs/super.c
parent4f331f01b9c43bf001d3ffee578a97a1e0633eac (diff)
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.c6
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:
305 if (s) { 305 if (s) {
306 up_write(&s->s_umount); 306 up_write(&s->s_umount);
307 destroy_super(s); 307 destroy_super(s);
308 s = NULL;
308 } 309 }
309 down_write(&old->s_umount); 310 down_write(&old->s_umount);
311 if (unlikely(!(old->s_flags & MS_BORN))) {
312 deactivate_locked_super(old);
313 goto retry;
314 }
310 return old; 315 return old;
311 } 316 }
312 } 317 }
@@ -918,6 +923,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
918 goto out_free_secdata; 923 goto out_free_secdata;
919 BUG_ON(!mnt->mnt_sb); 924 BUG_ON(!mnt->mnt_sb);
920 WARN_ON(!mnt->mnt_sb->s_bdi); 925 WARN_ON(!mnt->mnt_sb->s_bdi);
926 mnt->mnt_sb->s_flags |= MS_BORN;
921 927
922 error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata); 928 error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
923 if (error) 929 if (error)