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authorAl Viro <viro@zeniv.linux.org.uk>2012-01-03 21:01:29 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2012-01-03 22:53:10 -0500
commitdabe0dc194d5d56d379a8994fff47392744b6491 (patch)
tree16696a688d5b6386c6183cc6137807af38e1d9d1
parentcf31e70d6cf93f19fe9bf1144966ef40991ac723 (diff)
downloadlinux-dabe0dc194d5d56d379a8994fff47392744b6491.tar.bz2
vfs: fix the rest of sget() races
unfortunately, just checking MS_BORN after having grabbed ->s_umount in sget() is not enough; places that pick superblock from a list and grab s_umount shared need the same check in addition to checking for ->s_root; otherwise three-way race between failing mount, sget() and such list-walker can leave us with list-walker coming *second*, when temporary active ref grabbed by sget() (to be dropped when sget() notices that original mount has failed by checking MS_BORN) has lead to deactivate_locked_super() from failing ->mount() *not* doing ->kill_sb() and just releasing ->s_umount. Once sget() gets through and notices that MS_BORN had never been set it will drop the active ref and fs will be shut down and kicked out of all lists, but it's too late for something like sync_supers(). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/super.c20
1 files changed, 13 insertions, 7 deletions
diff --git a/fs/super.c b/fs/super.c
index bab11bad13ba..0413f51a9f0f 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -337,7 +337,7 @@ bool grab_super_passive(struct super_block *sb)
spin_unlock(&sb_lock);
if (down_read_trylock(&sb->s_umount)) {
- if (sb->s_root)
+ if (sb->s_root && (sb->s_flags & MS_BORN))
return true;
up_read(&sb->s_umount);
}
@@ -505,7 +505,7 @@ void sync_supers(void)
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
- if (sb->s_root && sb->s_dirt)
+ if (sb->s_root && sb->s_dirt && (sb->s_flags & MS_BORN))
sb->s_op->write_super(sb);
up_read(&sb->s_umount);
@@ -540,7 +540,7 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
- if (sb->s_root)
+ if (sb->s_root && (sb->s_flags & MS_BORN))
f(sb, arg);
up_read(&sb->s_umount);
@@ -575,7 +575,7 @@ void iterate_supers_type(struct file_system_type *type,
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
- if (sb->s_root)
+ if (sb->s_root && (sb->s_flags & MS_BORN))
f(sb, arg);
up_read(&sb->s_umount);
@@ -616,7 +616,7 @@ rescan:
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
/* still alive? */
- if (sb->s_root)
+ if (sb->s_root && (sb->s_flags & MS_BORN))
return sb;
up_read(&sb->s_umount);
/* nope, got unmounted */
@@ -676,7 +676,7 @@ rescan:
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
/* still alive? */
- if (sb->s_root)
+ if (sb->s_root && (sb->s_flags & MS_BORN))
return sb;
up_read(&sb->s_umount);
/* nope, got unmounted */
@@ -763,7 +763,8 @@ static void do_emergency_remount(struct work_struct *work)
sb->s_count++;
spin_unlock(&sb_lock);
down_write(&sb->s_umount);
- if (sb->s_root && sb->s_bdev && !(sb->s_flags & MS_RDONLY)) {
+ if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
+ !(sb->s_flags & MS_RDONLY)) {
/*
* What lock protects sb->s_flags??
*/
@@ -1146,6 +1147,11 @@ int freeze_super(struct super_block *sb)
return -EBUSY;
}
+ if (!(sb->s_flags & MS_BORN)) {
+ up_write(&sb->s_umount);
+ return 0; /* sic - it's "nothing to do" */
+ }
+
if (sb->s_flags & MS_RDONLY) {
sb->s_frozen = SB_FREEZE_TRANS;
smp_wmb();