path: root/drivers
diff options
authorSoren Hansen <soren@linux2go.dk>2011-02-10 15:01:28 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-02-11 16:12:20 -0800
commitde1f016f882e52facc3c8609599f827bcdd14af9 (patch)
tree0c542e3069eeb7920afaf659c46a86eeffa67fef /drivers
parent24a6f5b8589d2abfbf523c59ab1258726edc164f (diff)
nbd: remove module-level ioctl mutex
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>
Diffstat (limited to 'drivers')
1 files changed, 0 insertions, 3 deletions
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index a32fb41246f..e6fc716aca4 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);
error = __nbd_ioctl(bdev, lo, cmd, arg);
- mutex_unlock(&nbd_mutex);
return error;