nbd: Remove module-level ioctl mutex mistakenly introduced in 2.6.37

svn path=/dists/sid/linux-2.6/; revision=16888

debian/changelog

@@ -12,6 +12,7 @@ linux-2.6 (2.6.37-1) UNRELEASED; urgency=low
   * fs/notify: Enable FANOTIFY (Closes: #599877)
   * acer-wmi, aic94xx, asus_acpi, iscsi, janz-ican3, rtc-ds1511, tc1100-wmi:
     Restrict write permissions on files in procfs/sysfs
+  * nbd: Remove module-level ioctl mutex mistakenly introduced in 2.6.37
 
   [ Aurelien Jarno ]
   * [sh4] Export cpu_core_map to fix build failure with CONFIG_SFC=m.

debian/patches/bugfix/all/nbd-remove-module-level-ioctl-mutex.patch

@@ -0,0 +1,76 @@
+From: Soren Hansen <soren@linux2go.dk>
+Date: Thu, 10 Feb 2011 15:01:28 -0800
+Subject: [PATCH] nbd: remove module-level ioctl mutex
+
+commit de1f016f882e52facc3c8609599f827bcdd14af9 upstream.
+
+Commit 2a48fc0ab242417 ("block: autoconvert trivial BKL users to private
+mutex") replaced uses of the BKL in the nbd driver with mutex
+operations.  Since then, I've been been seeing these lock ups:
+
+ INFO: task qemu-nbd:16115 blocked for more than 120 seconds.
+ "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
+ qemu-nbd      D 0000000000000001     0 16115  16114 0x00000004
+  ffff88007d775d98 0000000000000082 ffff88007d775fd8 ffff88007d774000
+  0000000000013a80 ffff8800020347e0 ffff88007d775fd8 0000000000013a80
+  ffff880133730000 ffff880002034440 ffffea0004333db8 ffffffffa071c020
+ Call Trace:
+  [<ffffffff815b9997>] __mutex_lock_slowpath+0xf7/0x180
+  [<ffffffff815b93eb>] mutex_lock+0x2b/0x50
+  [<ffffffffa071a21c>] nbd_ioctl+0x6c/0x1c0 [nbd]
+  [<ffffffff812cb970>] blkdev_ioctl+0x230/0x730
+  [<ffffffff811967a1>] block_ioctl+0x41/0x50
+  [<ffffffff81175c03>] do_vfs_ioctl+0x93/0x370
+  [<ffffffff81175f61>] sys_ioctl+0x81/0xa0
+  [<ffffffff8100c0c2>] system_call_fastpath+0x16/0x1b
+
+Instrumenting the nbd module's ioctl handler with some extra logging
+clearly shows the NBD_DO_IT ioctl being invoked which is a long-lived
+ioctl in the sense that it doesn't return until another ioctl asks the
+driver to disconnect.  However, that other ioctl blocks, waiting for the
+module-level mutex that replaced the BKL, and then we're stuck.
+
+This patch removes the module-level mutex altogether.  It's clearly
+wrong, and as far as I can see, it's entirely unnecessary, since the nbd
+driver maintains per-device mutexes, and I don't see anything that would
+require a module-level (or kernel-level, for that matter) mutex.
+
+Signed-off-by: Soren Hansen <soren@linux2go.dk>
+Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
+Acked-by: Paul Clements <paul.clements@steeleye.com>
+Cc: Arnd Bergmann <arnd@arndb.de>
+Cc: Jens Axboe <axboe@kernel.dk>
+Cc: <stable@kernel.org>		[2.6.37.x]
+Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+---
+ drivers/block/nbd.c |    3 ---
+ 1 files changed, 0 insertions(+), 3 deletions(-)
+
+diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
+index a32fb41..e6fc716 100644
+--- a/drivers/block/nbd.c
++++ b/drivers/block/nbd.c
+@@ -53,7 +53,6 @@
+ #define DBG_BLKDEV      0x0100
+ #define DBG_RX          0x0200
+ #define DBG_TX          0x0400
+-static DEFINE_MUTEX(nbd_mutex);
+ static unsigned int debugflags;
+ #endif /* NDEBUG */
+ 
+@@ -718,11 +717,9 @@ static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
+ 	dprintk(DBG_IOCTL, "%s: nbd_ioctl cmd=%s(0x%x) arg=%lu\n",
+ 			lo->disk->disk_name, ioctl_cmd_to_ascii(cmd), cmd, arg);
+ 
+-	mutex_lock(&nbd_mutex);
+ 	mutex_lock(&lo->tx_lock);
+ 	error = __nbd_ioctl(bdev, lo, cmd, arg);
+ 	mutex_unlock(&lo->tx_lock);
+-	mutex_unlock(&nbd_mutex);
+ 
+ 	return error;
+ }
+-- 
+1.7.2.3
+

debian/patches/series/1

@@ -22,3 +22,4 @@
 + bugfix/all/rtc-rtc-ds1511-world-writable-sysfs-nvram-file.patch
 + bugfix/all/scsi-aic94xx-world-writable-sysfs-update_bios-file.patch
 + bugfix/all/scsi-iscsi-world-writable-sysfs-priv_sess-file.patch
++ bugfix/all/nbd-remove-module-level-ioctl-mutex.patch