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Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock
From: |
Igor Redko |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock |
Date: |
Mon, 28 Sep 2015 13:55:48 +0300 |
On Пт., 2015-09-25 at 17:46 +0800, Wen Congyang wrote:
> On 09/25/2015 05:09 PM, Denis V. Lunev wrote:
> > Release qemu global mutex before call synchronize_rcu().
> > synchronize_rcu() waiting for all readers to finish their critical
> > sections. There is at least one critical section in which we try
> > to get QGM (critical section is in address_space_rw() and
> > prepare_mmio_access() is trying to aquire QGM).
> >
> > Both functions (migration_end() and migration_bitmap_extend())
> > are called from main thread which is holding QGM.
> >
> > Thus there is a race condition that ends up with deadlock:
> > main thread working thread
> > Lock QGA |
> > | Call KVM_EXIT_IO handler
> > | |
> > | Open rcu reader's critical section
> > Migration cleanup bh |
> > | |
> > synchronize_rcu() is |
> > waiting for readers |
> > | prepare_mmio_access() is waiting for QGM
> > \ /
> > deadlock
> >
> > Patches here are quick and dirty, compile-tested only to validate the
> > architectual approach.
> >
> > Igor, Anna, can you pls start your tests with these patches instead of your
> > original one. Thank you.
>
> Can you give me the backtrace of the working thread?
>
> I think it is very bad to wait some lock in rcu reader's cirtical section.
#0 __lll_lock_wait () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1 0x00007f1ef113ccfd in __GI___pthread_mutex_lock (mutex=0x7f1ef4145ce0
<qemu_global_mutex>) at ../nptl/pthread_mutex_lock.c:80
#2 0x00007f1ef3c36546 in qemu_mutex_lock (mutex=0x7f1ef4145ce0
<qemu_global_mutex>) at util/qemu-thread-posix.c:73
#3 0x00007f1ef387ff46 in qemu_mutex_lock_iothread () at
/home/user/my_qemu/qemu/cpus.c:1170
#4 0x00007f1ef38514a2 in prepare_mmio_access (mr=0x7f1ef612f200) at
/home/user/my_qemu/qemu/exec.c:2390
#5 0x00007f1ef385157e in address_space_rw (as=0x7f1ef40ec940
<address_space_io>, addr=49402, attrs=..., buf=0x7f1ef3f97000 "\001", len=1,
is_write=true)
at /home/user/my_qemu/qemu/exec.c:2425
#6 0x00007f1ef3897c53 in kvm_handle_io (port=49402, attrs=...,
data=0x7f1ef3f97000, direction=1, size=1, count=1) at
/home/user/my_qemu/qemu/kvm-all.c:1680
#7 0x00007f1ef3898144 in kvm_cpu_exec (cpu=0x7f1ef5010fc0) at
/home/user/my_qemu/qemu/kvm-all.c:1849
#8 0x00007f1ef387fa91 in qemu_kvm_cpu_thread_fn (arg=0x7f1ef5010fc0) at
/home/user/my_qemu/qemu/cpus.c:979
#9 0x00007f1ef113a6aa in start_thread (arg=0x7f1eef0b9700) at
pthread_create.c:333
#10 0x00007f1ef0e6feed in clone () at
../sysdeps/unix/sysv/linux/x86_64/clone.S:109
>
> >
> > Signed-off-by: Denis V. Lunev <address@hidden>
> > CC: Igor Redko <address@hidden>
> > CC: Anna Melekhova <address@hidden>
> > CC: Juan Quintela <address@hidden>
> > CC: Amit Shah <address@hidden>
> >
> > Denis V. Lunev (2):
> > migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0
> > migration: fix deadlock
> >
> > migration/ram.c | 45 ++++++++++++++++++++++++++++-----------------
> > 1 file changed, 28 insertions(+), 17 deletions(-)
> >
>
- Re: [Qemu-devel] [PATCH 1/1] migration: fix deadlock, (continued)
- Re: [Qemu-devel] [PATCH 1/1] migration: fix deadlock, Wen Congyang, 2015/09/25
- [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock, Denis V. Lunev, 2015/09/25
- [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0, Denis V. Lunev, 2015/09/25
- Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0, Wen Congyang, 2015/09/25
- Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0, Denis V. Lunev, 2015/09/25
- Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0, Wen Congyang, 2015/09/25
- Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0, Denis V. Lunev, 2015/09/25
- [Qemu-devel] [PATCH 2/2] migration: fix deadlock, Denis V. Lunev, 2015/09/25
- Re: [Qemu-devel] [PATCH 2/2] migration: fix deadlock, Wen Congyang, 2015/09/25
- Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock, Wen Congyang, 2015/09/25
- Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock,
Igor Redko <=
- Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock, Igor Redko, 2015/09/29
[Qemu-devel] [PATCH 1/1] migration: fix deadlock, Denis V. Lunev, 2015/09/28