Re: [Qemu-devel] [BUG] I/O thread segfault for QEMU on s390x

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Mar 01, 2018 at 09:33:35AM -0500, Farhan Ali wrote:
> Hi,
> 
> I have been noticing some segfaults for QEMU on s390x, and I have been
> hitting this issue quite reliably (at least once in 10 runs of a test case).
> The qemu version is 2.11.50, and I have systemd created coredumps
> when this happens.
> 
> Here is a back trace of the segfaulting thread:

The backtrace looks normal.

Please post the QEMU command-line and the details of the segfault (which
memory access faulted?).

> #0  0x000003ffafed202c in swapcontext () from /lib64/libc.so.6
> #1  0x000002aa355c02ee in qemu_coroutine_new () at
> util/coroutine-ucontext.c:164
> #2  0x000002aa355bec34 in qemu_coroutine_create
> (entry=entry@entry=0x2aa3550f7a8 <blk_aio_read_entry>,
> opaque=opaque@entry=0x3ffa002afa0) at util/qemu-coroutine.c:76
> #3  0x000002aa35510262 in blk_aio_prwv (blk=0x2aa65fbefa0, offset=<optimized
> out>, bytes=<optimized out>, qiov=0x3ffa002a9c0,
> co_entry=co_entry@entry=0x2aa3550f7a8 <blk_aio_read_entry>, flags=0,
>     cb=0x2aa35340a50 <virtio_blk_rw_complete>, opaque=0x3ffa002a960) at
> block/block-backend.c:1299
> #4  0x000002aa35510376 in blk_aio_preadv (blk=<optimized out>,
> offset=<optimized out>, qiov=<optimized out>, flags=<optimized out>,
> cb=<optimized out>, opaque=0x3ffa002a960) at block/block-backend.c:1392
> #5  0x000002aa3534114e in submit_requests (niov=<optimized out>,
> num_reqs=<optimized out>, start=<optimized out>, mrb=<optimized out>,
> blk=<optimized out>) at
> /usr/src/debug/qemu-2.11.50/hw/block/virtio-blk.c:372
> #6  virtio_blk_submit_multireq (blk=<optimized out>,
> mrb=mrb@entry=0x3ffad77e640) at
> /usr/src/debug/qemu-2.11.50/hw/block/virtio-blk.c:402
> #7  0x000002aa353422e0 in virtio_blk_handle_vq (s=0x2aa6611e7d8,
> vq=0x3ffb0f5f010) at /usr/src/debug/qemu-2.11.50/hw/block/virtio-blk.c:620
> #8  0x000002aa3536655a in virtio_queue_notify_aio_vq
> (vq=vq@entry=0x3ffb0f5f010) at
> /usr/src/debug/qemu-2.11.50/hw/virtio/virtio.c:1515
> #9  0x000002aa35366cd6 in virtio_queue_notify_aio_vq (vq=0x3ffb0f5f010) at
> /usr/src/debug/qemu-2.11.50/hw/virtio/virtio.c:1511
> #10 virtio_queue_host_notifier_aio_poll (opaque=0x3ffb0f5f078) at
> /usr/src/debug/qemu-2.11.50/hw/virtio/virtio.c:2409
> #11 0x000002aa355a8ba4 in run_poll_handlers_once
> (ctx=ctx@entry=0x2aa65f99310) at util/aio-posix.c:497
> #12 0x000002aa355a9b74 in run_poll_handlers (max_ns=<optimized out>,
> ctx=0x2aa65f99310) at util/aio-posix.c:534
> #13 try_poll_mode (blocking=true, ctx=0x2aa65f99310) at util/aio-posix.c:562
> #14 aio_poll (ctx=0x2aa65f99310, blocking=blocking@entry=true) at
> util/aio-posix.c:602
> #15 0x000002aa353d2d0a in iothread_run (opaque=0x2aa65f990f0) at
> iothread.c:60
> #16 0x000003ffb0f07e82 in start_thread () from /lib64/libpthread.so.0
> #17 0x000003ffaff91596 in thread_start () from /lib64/libc.so.6
> 
> 
> I don't have much knowledge about i/o threads and the block layer code in
> QEMU, so I would like to report to the community about this issue.
> I believe this very similar to the bug that I reported upstream couple of
> days ago
> (https://lists.gnu.org/archive/html/qemu-devel/2018-02/msg04452.html).
> 
> Any help would be greatly appreciated.
> 
> Thanks
> Farhan
> 

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