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


From: Farhan Ali
Subject: [Qemu-devel] [BUG] I/O thread segfault for QEMU on s390x
Date: Thu, 1 Mar 2018 09:33:35 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

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:


#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 (address@hidden <blk_aio_read_entry>, address@hidden) at util/qemu-coroutine.c:76 #3 0x000002aa35510262 in blk_aio_prwv (blk=0x2aa65fbefa0, offset=<optimized out>, bytes=<optimized out>, qiov=0x3ffa002a9c0, address@hidden <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>, address@hidden) 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 (address@hidden) 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 (address@hidden) 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, address@hidden) 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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