* [PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw
2012-02-10 10:02 [PATCH 0/2 v2] Fix deadlock with suspend & quotas Jan Kara
@ 2012-02-10 10:03 ` Jan Kara
2012-02-12 21:13 ` Al Viro
2012-02-10 10:03 ` [PATCH 2/2] quota: Fix deadlock with suspend and quotas Jan Kara
1 sibling, 1 reply; 5+ messages in thread
From: Jan Kara @ 2012-02-10 10:03 UTC (permalink / raw)
To: Al Viro
Cc: LKML, linux-fsdevel, Dave Chinner, mpatocka, Eric Sandeen, Jan Kara
In quota code we need to find a superblock corresponding to a device and wait
for superblock to be unfrozen. However this waiting has to happen without
s_umount semaphore because that is required for superblock to thaw. So provide
a function in VFS for this to keep dances with s_umount where they belong.
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/super.c | 50 ++++++++++++++++++++++++++++++++++++++------------
include/linux/fs.h | 1 +
2 files changed, 39 insertions(+), 12 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index 6015c02..1f657d6 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -593,15 +593,8 @@ void iterate_supers_type(struct file_system_type *type,
EXPORT_SYMBOL(iterate_supers_type);
-/**
- * get_super - get the superblock of a device
- * @bdev: device to get the superblock for
- *
- * Scans the superblock list and finds the superblock of the file system
- * mounted on the device given. %NULL is returned if no match is found.
- */
-
-struct super_block *get_super(struct block_device *bdev)
+static struct super_block *__get_super(struct block_device *bdev,
+ bool wait_thaw)
{
struct super_block *sb;
@@ -618,9 +611,13 @@ rescan:
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
/* still alive? */
- if (sb->s_root && (sb->s_flags & MS_BORN))
- return sb;
- up_read(&sb->s_umount);
+ if (sb->s_root && (sb->s_flags & MS_BORN)) {
+ if (!wait_thaw || sb->s_frozen == SB_UNFROZEN)
+ return sb;
+ up_read(&sb->s_umount);
+ vfs_check_frozen(sb, SB_FREEZE_WRITE);
+ } else
+ up_read(&sb->s_umount);
/* nope, got unmounted */
spin_lock(&sb_lock);
__put_super(sb);
@@ -631,9 +628,38 @@ rescan:
return NULL;
}
+/**
+ * get_super - get the superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given. %NULL is returned if no match is found.
+ * Note that the returned superblock may be frozen.
+ */
+
+struct super_block *get_super(struct block_device *bdev)
+{
+ return __get_super(bdev, false);
+}
EXPORT_SYMBOL(get_super);
/**
+ * get_super_thawed - get thawed superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device. The superblock is returned once it is thawed
+ * (or immediately if it was not frozen). %NULL is returned if no match
+ * is found.
+ */
+
+struct super_block *get_super_thawed(struct block_device *bdev)
+{
+ return __get_super(bdev, true);
+}
+EXPORT_SYMBOL(get_super_thawed);
+
+/**
* get_active_super - get an active reference to the superblock of a device
* @bdev: device to get the superblock for
*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 386da09..69cd5bb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2496,6 +2496,7 @@ extern void get_filesystem(struct file_system_type *fs);
extern void put_filesystem(struct file_system_type *fs);
extern struct file_system_type *get_fs_type(const char *name);
extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_thawed(struct block_device *);
extern struct super_block *get_active_super(struct block_device *bdev);
extern void drop_super(struct super_block *sb);
extern void iterate_supers(void (*)(struct super_block *, void *), void *);
--
1.7.1
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH 2/2] quota: Fix deadlock with suspend and quotas
2012-02-10 10:02 [PATCH 0/2 v2] Fix deadlock with suspend & quotas Jan Kara
2012-02-10 10:03 ` [PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw Jan Kara
@ 2012-02-10 10:03 ` Jan Kara
1 sibling, 0 replies; 5+ messages in thread
From: Jan Kara @ 2012-02-10 10:03 UTC (permalink / raw)
To: Al Viro
Cc: LKML, linux-fsdevel, Dave Chinner, mpatocka, Eric Sandeen, Jan Kara
This script causes a kernel deadlock:
set -e
DEVICE=/dev/vg1/linear
lvchange -ay $DEVICE
mkfs.ext3 $DEVICE
mount -t ext3 -o usrquota,grpquota $DEVICE /mnt/test
quotacheck -gu /mnt/test
umount /mnt/test
mount -t ext3 -o usrquota,grpquota $DEVICE /mnt/test
quotaon /mnt/test
dmsetup suspend $DEVICE
setquota -u root 1 2 3 4 /mnt/test &
sleep 1
dmsetup resume $DEVICE
setquota acquired semaphore s_umount for read and then tried to perform a
transaction (and waits because the device is suspended). dmsetup resume tries
to acquire s_umount for write before resuming the device (and waits for
setquota).
Fix the deadlock by grabbing a thawed superblock for quota commands which need
it.
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/quota/quota.c | 24 +++++++++++++++++++++---
1 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index 7898cd6..fc2c438 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -292,11 +292,26 @@ static int do_quotactl(struct super_block *sb, int type, int cmd, qid_t id,
}
}
+/* Return 1 if 'cmd' will block on frozen filesystem */
+static int quotactl_cmd_write(int cmd)
+{
+ switch (cmd) {
+ case Q_GETFMT:
+ case Q_GETINFO:
+ case Q_SYNC:
+ case Q_XGETQSTAT:
+ case Q_XGETQUOTA:
+ case Q_XQUOTASYNC:
+ return 0;
+ }
+ return 1;
+}
+
/*
* look up a superblock on which quota ops will be performed
* - use the name of a block device to find the superblock thereon
*/
-static struct super_block *quotactl_block(const char __user *special)
+static struct super_block *quotactl_block(const char __user *special, int cmd)
{
#ifdef CONFIG_BLOCK
struct block_device *bdev;
@@ -309,7 +324,10 @@ static struct super_block *quotactl_block(const char __user *special)
putname(tmp);
if (IS_ERR(bdev))
return ERR_CAST(bdev);
- sb = get_super(bdev);
+ if (quotactl_cmd_write(cmd))
+ sb = get_super_thawed(bdev);
+ else
+ sb = get_super(bdev);
bdput(bdev);
if (!sb)
return ERR_PTR(-ENODEV);
@@ -361,7 +379,7 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
pathp = &path;
}
- sb = quotactl_block(special);
+ sb = quotactl_block(special, cmds);
if (IS_ERR(sb)) {
ret = PTR_ERR(sb);
goto out;
--
1.7.1
^ permalink raw reply [flat|nested] 5+ messages in thread