From de1f016f882e52facc3c8609599f827bcdd14af9 Mon Sep 17 00:00:00 2001 From: Soren Hansen Date: Thu, 10 Feb 2011 15:01:28 -0800 Subject: [PATCH] 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: [] __mutex_lock_slowpath+0xf7/0x180 [] mutex_lock+0x2b/0x50 [] nbd_ioctl+0x6c/0x1c0 [nbd] [] blkdev_ioctl+0x230/0x730 [] block_ioctl+0x41/0x50 [] do_vfs_ioctl+0x93/0x370 [] sys_ioctl+0x81/0xa0 [] 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 Acked-by: Serge Hallyn Acked-by: Paul Clements Cc: Arnd Bergmann Cc: Jens Axboe Cc: [2.6.37.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/nbd.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index a32fb41246f883..e6fc716aca4521 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; }