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