The patch titled nbd: remove module-level ioctl mutex has been added to the -mm tree. Its filename is nbd-remove-module-level-ioctl-mutex.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: nbd: remove module-level ioctl mutex From: Soren Hansen <soren@xxxxxxxxxxx> 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 [<ffffffff81132f13>] ? handle_mm_fault+0x1c3/0x410 [<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 [<ffffffff8116fa83>] ? putname+0x33/0x50 [<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@xxxxxxxxxxx> Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx> Acked-by: Paul Clements <paul.clements@xxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/block/nbd.c | 3 --- 1 file changed, 3 deletions(-) diff -puN drivers/block/nbd.c~nbd-remove-module-level-ioctl-mutex drivers/block/nbd.c --- a/drivers/block/nbd.c~nbd-remove-module-level-ioctl-mutex +++ a/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 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; } _ Patches currently in -mm which might be from soren@xxxxxxxxxxx are nbd-remove-module-level-ioctl-mutex.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html