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Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock
From: |
Wen Congyang |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock |
Date: |
Fri, 25 Sep 2015 17:46:35 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 |
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.
To Paolo:
Do we allow this in rcu critical section?
Thanks
Wen Congyang
>
> 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, Denis V. Lunev, 2015/09/25
- 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 <=
- Re: [Qemu-devel] [PATCH v2 0/2] migration: fix deadlock, Igor Redko, 2015/09/29
- 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