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Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock |
Date: |
Tue, 29 Sep 2015 09:47:16 +0100 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
* Igor Redko (address@hidden) wrote:
> 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
Do you have a test to run in the guest that easily triggers this?
Dave
> >
> > >
> > > 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(-)
> > >
> >
>
>
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock,
Dr. David Alan Gilbert <=