e091f0e905
In qemu_laio_process_completions_and_submit, the AioContext is acquired before the ioq_submit iteration and after qemu_laio_process_completions, but the latter is not thread safe either. This change avoids a number of random crashes when the Main Thread and an IO Thread collide processing completions for the same AioContext. This is an example of such crash: - The IO Thread is trying to acquire the AioContext at aio_co_enter, which evidences that it didn't lock it before: Thread 3 (Thread 0x7fdfd8bd8700 (LWP 36743)): #0 0x00007fdfe0dd542d in __lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135 #1 0x00007fdfe0dd0de6 in _L_lock_870 () at /lib64/libpthread.so.0 #2 0x00007fdfe0dd0cdf in __GI___pthread_mutex_lock (mutex=mutex@entry=0x5631fde0e6c0) at ../nptl/pthread_mutex_lock.c:114 #3 0x00005631fc0603a7 in qemu_mutex_lock_impl (mutex=0x5631fde0e6c0, file=0x5631fc23520f "util/async.c", line=511) at util/qemu-thread-posix.c:66 #4 0x00005631fc05b558 in aio_co_enter (ctx=0x5631fde0e660, co=0x7fdfcc0c2b40) at util/async.c:493 #5 0x00005631fc05b5ac in aio_co_wake (co=<optimized out>) at util/async.c:478 #6 0x00005631fbfc51ad in qemu_laio_process_completion (laiocb=<optimized out>) at block/linux-aio.c:104 #7 0x00005631fbfc523c in qemu_laio_process_completions (s=s@entry=0x7fdfc0297670) at block/linux-aio.c:222 #8 0x00005631fbfc5499 in qemu_laio_process_completions_and_submit (s=0x7fdfc0297670) at block/linux-aio.c:237 #9 0x00005631fc05d978 in aio_dispatch_handlers (ctx=ctx@entry=0x5631fde0e660) at util/aio-posix.c:406 #10 0x00005631fc05e3ea in aio_poll (ctx=0x5631fde0e660, blocking=blocking@entry=true) at util/aio-posix.c:693 #11 0x00005631fbd7ad96 in iothread_run (opaque=0x5631fde0e1c0) at iothread.c:64 #12 0x00007fdfe0dcee25 in start_thread (arg=0x7fdfd8bd8700) at pthread_create.c:308 #13 0x00007fdfe0afc34d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:113 - The Main Thread is also processing completions from the same AioContext, and crashes due to failed assertion at util/iov.c:78: Thread 1 (Thread 0x7fdfeb5eac80 (LWP 36740)): #0 0x00007fdfe0a391f7 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 #1 0x00007fdfe0a3a8e8 in __GI_abort () at abort.c:90 #2 0x00007fdfe0a32266 in __assert_fail_base (fmt=0x7fdfe0b84e68 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=assertion@entry=0x5631fc238ccb "offset == 0", file=file@entry=0x5631fc23698e "util/iov.c", line=line@entry=78, function=function@entry=0x5631fc236adc <__PRETTY_FUNCTION__.15220> "iov_memset") at assert.c:92 #3 0x00007fdfe0a32312 in __GI___assert_fail (assertion=assertion@entry=0x5631fc238ccb "offset == 0", file=file@entry=0x5631fc23698e "util/iov.c", line=line@entry=78, function=function@entry=0x5631fc236adc <__PRETTY_FUNCTION__.15220> "iov_memset") at assert.c:101 #4 0x00005631fc065287 in iov_memset (iov=<optimized out>, iov_cnt=<optimized out>, offset=<optimized out>, offset@entry=65536, fillc=fillc@entry=0, bytes=15515191315812405248) at util/iov.c:78 #5 0x00005631fc065a63 in qemu_iovec_memset (qiov=<optimized out>, offset=offset@entry=65536, fillc=fillc@entry=0, bytes=<optimized out>) at util/iov.c:410 #6 0x00005631fbfc5178 in qemu_laio_process_completion (laiocb=0x7fdd920df630) at block/linux-aio.c:88 #7 0x00005631fbfc523c in qemu_laio_process_completions (s=s@entry=0x7fdfc0297670) at block/linux-aio.c:222 #8 0x00005631fbfc5499 in qemu_laio_process_completions_and_submit (s=0x7fdfc0297670) at block/linux-aio.c:237 #9 0x00005631fbfc54ed in qemu_laio_poll_cb (opaque=<optimized out>) at block/linux-aio.c:272 #10 0x00005631fc05d85e in run_poll_handlers_once (ctx=ctx@entry=0x5631fde0e660) at util/aio-posix.c:497 #11 0x00005631fc05e2ca in aio_poll (blocking=false, ctx=0x5631fde0e660) at util/aio-posix.c:574 #12 0x00005631fc05e2ca in aio_poll (ctx=0x5631fde0e660, blocking=blocking@entry=false) at util/aio-posix.c:604 #13 0x00005631fbfcb8a3 in bdrv_do_drained_begin (ignore_parent=<optimized out>, recursive=<optimized out>, bs=<optimized out>) at block/io.c:273 #14 0x00005631fbfcb8a3 in bdrv_do_drained_begin (bs=0x5631fe8b6200, recursive=<optimized out>, parent=0x0, ignore_bds_parents=<optimized out>, poll=<optimized out>) at block/io.c:390 #15 0x00005631fbfbcd2e in blk_drain (blk=0x5631fe83ac80) at block/block-backend.c:1590 #16 0x00005631fbfbe138 in blk_remove_bs (blk=blk@entry=0x5631fe83ac80) at block/block-backend.c:774 #17 0x00005631fbfbe3d6 in blk_unref (blk=0x5631fe83ac80) at block/block-backend.c:401 #18 0x00005631fbfbe3d6 in blk_unref (blk=0x5631fe83ac80) at block/block-backend.c:449 #19 0x00005631fbfc9a69 in commit_complete (job=0x5631fe8b94b0, opaque=0x7fdfcc1bb080) at block/commit.c:92 #20 0x00005631fbf7d662 in job_defer_to_main_loop_bh (opaque=0x7fdfcc1b4560) at job.c:973 #21 0x00005631fc05ad41 in aio_bh_poll (bh=0x7fdfcc01ad90) at util/async.c:90 #22 0x00005631fc05ad41 in aio_bh_poll (ctx=ctx@entry=0x5631fddffdb0) at util/async.c:118 #23 0x00005631fc05e210 in aio_dispatch (ctx=0x5631fddffdb0) at util/aio-posix.c:436 #24 0x00005631fc05ac1e in aio_ctx_dispatch (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at util/async.c:261 #25 0x00007fdfeaae44c9 in g_main_context_dispatch (context=0x5631fde00140) at gmain.c:3201 #26 0x00007fdfeaae44c9 in g_main_context_dispatch (context=context@entry=0x5631fde00140) at gmain.c:3854 #27 0x00005631fc05d503 in main_loop_wait () at util/main-loop.c:215 #28 0x00005631fc05d503 in main_loop_wait (timeout=<optimized out>) at util/main-loop.c:238 #29 0x00005631fc05d503 in main_loop_wait (nonblocking=nonblocking@entry=0) at util/main-loop.c:497 #30 0x00005631fbd81412 in main_loop () at vl.c:1866 #31 0x00005631fbc18ff3 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4647 - A closer examination shows that s->io_q.in_flight appears to have gone backwards: (gdb) frame 7 #7 0x00005631fbfc523c in qemu_laio_process_completions (s=s@entry=0x7fdfc0297670) at block/linux-aio.c:222 222 qemu_laio_process_completion(laiocb); (gdb) p s $2 = (LinuxAioState *) 0x7fdfc0297670 (gdb) p *s $3 = {aio_context = 0x5631fde0e660, ctx = 0x7fdfeb43b000, e = {rfd = 33, wfd = 33}, io_q = {plugged = 0, in_queue = 0, in_flight = 4294967280, blocked = false, pending = {sqh_first = 0x0, sqh_last = 0x7fdfc0297698}}, completion_bh = 0x7fdfc0280ef0, event_idx = 21, event_max = 241} (gdb) p/x s->io_q.in_flight $4 = 0xfffffff0 Signed-off-by: Sergio Lopez <slp@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com> |
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accel | ||
audio | ||
backends | ||
block | ||
bsd-user | ||
capstone@22ead3e0bf | ||
chardev | ||
contrib | ||
crypto | ||
default-configs | ||
disas | ||
docs | ||
dtc@e54388015a | ||
fpu | ||
fsdev | ||
gdb-xml | ||
hw | ||
include | ||
io | ||
libdecnumber | ||
linux-headers | ||
linux-user | ||
migration | ||
nbd | ||
net | ||
pc-bios | ||
po | ||
qapi | ||
qga | ||
qobject | ||
qom | ||
replay | ||
roms | ||
scripts | ||
scsi | ||
slirp | ||
stubs | ||
target | ||
tcg | ||
tests | ||
trace | ||
ui | ||
util | ||
.dir-locals.el | ||
.editorconfig | ||
.exrc | ||
.gdbinit | ||
.gitignore | ||
.gitmodules | ||
.gitpublish | ||
.mailmap | ||
.shippable.yml | ||
.travis.yml | ||
arch_init.c | ||
balloon.c | ||
block.c | ||
blockdev-nbd.c | ||
blockdev.c | ||
blockjob.c | ||
bootdevice.c | ||
bt-host.c | ||
bt-vhci.c | ||
Changelog | ||
CODING_STYLE | ||
configure | ||
COPYING | ||
COPYING.LIB | ||
cpus-common.c | ||
cpus.c | ||
device_tree.c | ||
device-hotplug.c | ||
disas.c | ||
dma-helpers.c | ||
dump.c | ||
exec.c | ||
gdbstub.c | ||
HACKING | ||
hmp-commands-info.hx | ||
hmp-commands.hx | ||
hmp.c | ||
hmp.h | ||
ioport.c | ||
iothread.c | ||
job-qmp.c | ||
job.c | ||
LICENSE | ||
MAINTAINERS | ||
Makefile | ||
Makefile.objs | ||
Makefile.target | ||
memory_ldst.inc.c | ||
memory_mapping.c | ||
memory.c | ||
module-common.c | ||
monitor.c | ||
numa.c | ||
os-posix.c | ||
os-win32.c | ||
qdev-monitor.c | ||
qdict-test-data.txt | ||
qemu-bridge-helper.c | ||
qemu-deprecated.texi | ||
qemu-doc.texi | ||
qemu-ga.texi | ||
qemu-img-cmds.hx | ||
qemu-img.c | ||
qemu-img.texi | ||
qemu-io-cmds.c | ||
qemu-io.c | ||
qemu-keymap.c | ||
qemu-nbd.c | ||
qemu-nbd.texi | ||
qemu-option-trace.texi | ||
qemu-options-wrapper.h | ||
qemu-options.h | ||
qemu-options.hx | ||
qemu-seccomp.c | ||
qemu-tech.texi | ||
qemu.nsi | ||
qemu.sasl | ||
qmp.c | ||
qtest.c | ||
README | ||
replication.c | ||
replication.h | ||
rules.mak | ||
thunk.c | ||
tpm.c | ||
trace-events | ||
VERSION | ||
version.rc | ||
vl.c | ||
win_dump.c | ||
win_dump.h |
QEMU README =========== QEMU is a generic and open source machine & userspace emulator and virtualizer. QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board). QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation. QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager. QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file. Building ======== QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: mkdir build cd build ../configure make Additional information can also be found online via the QEMU website: https://qemu.org/Hosts/Linux https://qemu.org/Hosts/Mac https://qemu.org/Hosts/W32 Submitting patches ================== The QEMU source code is maintained under the GIT version control system. git clone git://git.qemu.org/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the HACKING and CODING_STYLE files. Additional information on submitting patches can be found online via the QEMU website https://qemu.org/Contribute/SubmitAPatch https://qemu.org/Contribute/TrivialPatches The QEMU website is also maintained under source control. git clone git://git.qemu.org/qemu-web.git https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once. For installation instructions, please go to https://github.com/stefanha/git-publish The workflow with 'git-publish' is: $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future. Sending v2: $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2. Bug reporting ============= The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs found when running code built from QEMU git or upstream released sources should be reported via: https://bugs.launchpad.net/qemu/ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via launchpad. For additional information on bug reporting consult: https://qemu.org/Contribute/ReportABug Contact ======= The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC - qemu-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/qemu-devel - #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: https://qemu.org/Contribute/StartHere -- End