[PATCH] Linux-2.4.18 block MTD dead-lock
Takeharu KATO
tkato at cs.fujitsu.co.jp
Tue Nov 26 08:04:32 EST 2002
MTD developers:
I found a bug relevant to MTD device and Linux-2.4.18.
I post the report about the issue.
P.S. I attach the patch to fix this problem.
If you have no time to read following report.
please see this patch.
-- the report --
1. The symptom
When we was trying to mount MTD-block-device twice,
second mount process fall in dead-locked state. This
is due not to be able to obtain the semaphore of
the superblock().
We met this with Linux-2.4.18 kernel on PPC405GP.
This issue has never taken place with Linux-2.4.2.
2. The reason
We found this was caused in the release method of
MTD. In particular, this method indirectly call
sync_super with calling ``invalidate_device''
in this method.
When the kernel attempt to mount the block device,
it call ``get_sb_bdev'' function in fs/super.c. This
function return the super block information to caller
and this function perform following operations.
Step1. Open the block device to be mounted.
Step2. Obtain semaphore of the super block to
update super block information.
Step3. Search the block device in super block list
for mounted devices.
Step4. If the device has been already mounted,
it close the block device using its release
method then return the super block information.
Step5 If the device has not been mounted yet,
the file system read the super block from
the device and return the information.
The reason of the deadlock is that the process
keep waiting for the semaphore owned by itself
when it call MTD release method.
The process has already obtained the semaphore since
the Step2 was performed.
3. The solution
We changed the sequence of the function called ``get_sb_bdev''
in fs/super.c. We changed the function to make the block device
to be mounted checked before opening the device.
Please refer the patch to make out the changes in detail.
-- the report --
Sincerely, yours.
--
Takeharu KATO
Fujitsu Limited
Email:tkato at cs.fujitsu.co.jp (ext. 7112-4621)
-------------- next part --------------
--- linux-2.4.18/fs/super.c Tue Mar 12 15:04:10 2002
+++ linux-2.4.18-getsbfix/fs/super.c Tue Nov 26 21:58:02 2002
@@ -15,7 +15,7 @@
* Added kerneld support: Jacques Gelinas and Bjorn Ekwall
* Added change_root: Werner Almesberger & Hans Lermen, Feb '96
* Added options to /proc/mounts:
- * Torbjörn Lindh (torbjorn.lindh at gopta.se), April 14, 1996.
+ * Torbj-Aörn Lindh (torbjorn.lindh at gopta.se), April 14, 1996.$)B
* Added devfs support: Richard Gooch <rgooch at atnf.csiro.au>, 13-JAN-1998
* Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
*/
@@ -645,21 +645,16 @@
dev = to_kdev_t(bdev->bd_dev);
if (!(flags & MS_RDONLY))
mode |= FMODE_WRITE;
- error = blkdev_get(bdev, mode, 0, BDEV_FS);
- devfs_put_ops (de); /* Decrement module use count now we're safe */
- if (error)
- goto out;
check_disk_change(dev);
error = -EACCES;
if (!(flags & MS_RDONLY) && is_read_only(dev)) {
- blkdev_put(bdev, BDEV_FS);
+ devfs_put_ops (de); /* Decrement module use count */
goto out;
}
-
error = -ENOMEM;
s = alloc_super();
if (!s) {
- blkdev_put(bdev, BDEV_FS);
+ devfs_put_ops (de); /* Decrement module use count */
goto out;
}
@@ -675,16 +670,24 @@
((flags ^ old->s_flags) & MS_RDONLY)) {
spin_unlock(&sb_lock);
destroy_super(s);
- blkdev_put(bdev, BDEV_FS);
+ devfs_put_ops (de); /* Decrement module use count */
goto out;
}
if (!grab_super(old))
goto restart;
destroy_super(s);
- blkdev_put(bdev, BDEV_FS);
+ devfs_put_ops (de); /* Decrement module use count */
path_release(&nd);
return old;
}
+ /*
+ * 2002.11.08 moved by T. KATO
+ * To make MTD worked.
+ */
+ error = blkdev_get(bdev, mode, 0, BDEV_FS);
+ devfs_put_ops (de); /* Decrement module use count now we're safe */
+ if (error)
+ goto out;
s->s_dev = dev;
s->s_bdev = bdev;
s->s_flags = flags;
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