Hang in 9p/virtio

[Vegard Nossum]

Hi,

With fault injection triggering an allocation failure for the
alloc_indirect() call in virtqueue_add() I'm seeing a hang in
p9_virtio_zc_request() -- it seems to be waiting here indefinitely
(i.e. at least 120 seconds):

        err = wait_event_interruptible(*req->wq,
                                       req->status >= REQ_STATUS_RCVD);

Maybe somebody who is already familiar with the could would have a look?

Stack trace for the memory allocation failure:

CPU: 2 PID: 3877 Comm: trinity-c2 Not tainted 4.7.0+ #70
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
Ubuntu-1.8.2-1ubuntu1 04/01/2014
 ffffffff84354a78 ffff88010594f2e8 ffffffff81d72f91 ffffffff84354a60
 1ffff10020b29e62 ffff88010594f398 ffffffff81e07df7 00007faad2003fff
 0000000000000064 ffffffffffffffff 0000000041b58ab3 ffffffff840a481c
Call Trace:
 [...]
 [<ffffffff81473886>] __kmalloc+0x66/0x2e0
 [<ffffffff81f7c6b4>] alloc_indirect.isra.8+0x24/0xa0
 [<ffffffff81f7d37f>] virtqueue_add_sgs+0x41f/0xc90
 [<ffffffff836eb281>] p9_virtio_zc_request+0x531/0xdb0
 [<ffffffff836d6ecf>] p9_client_zc_rpc.constprop.14+0x23f/0xe80
 [<ffffffff836db77c>] p9_client_read+0x4bc/0x8d0
 [<ffffffff8193f0a3>] v9fs_file_read_iter+0xd3/0x190
 [<ffffffff814b4b62>] do_iter_readv_writev+0x212/0x490
 [<ffffffff814b6be9>] do_readv_writev+0x359/0x660
 [<ffffffff814babc7>] vfs_readv+0x67/0xa0
 [<ffffffff814bacd8>] do_readv+0xd8/0x270

Stack trace for the stuck call:

NMI backtrace for cpu 2
CPU: 2 PID: 3877 Comm: trinity-c2 Not tainted 4.7.0+ #70
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 
Ubuntu-1.8.2-1ubuntu1 04/01/2014
task: ffff8801174f5b00 task.stack: ffff880105948000
RIP: 0010:[<ffffffff810b02a0>]  [<ffffffff810b02a0>] 
__default_send_IPI_dest_field+0xe0/0x130
Call Trace:
 [...]
 [<ffffffff811d584e>] prepare_to_wait_event+0x19e/0x410
 [<ffffffff836eb790>] p9_virtio_zc_request+0xa40/0xdb0
 [<ffffffff836d6ecf>] p9_client_zc_rpc.constprop.14+0x23f/0xe80
 [<ffffffff836db77c>] p9_client_read+0x4bc/0x8d0
 [<ffffffff8193f0a3>] v9fs_file_read_iter+0xd3/0x190
 [<ffffffff814b4b62>] do_iter_readv_writev+0x212/0x490
 [<ffffffff814b6be9>] do_readv_writev+0x359/0x660
 [<ffffffff814babc7>] vfs_readv+0x67/0xa0
 [<ffffffff814bacd8>] do_readv+0xd8/0x270


Vegard