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Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly syn
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized |
Date: |
Wed, 25 Nov 2015 15:36:49 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 25/11/2015 15:04, David Engraf wrote:
>>>
>>
>> No, you don't. Who is reading iothread_locked during
>> qemu_cond_wait_iothread? No one, because it is a thread-local variable
>> whose address is never taken.
>
> prepare_mmio_access is reading iothread_locked by using
> qemu_mutex_iothread_locked after qemu_tcg_wait_io_event calls
> qemu_cond_wait. All one the same thread.
Sure, but who has set iothread_locked to false during the execution of
qemu_cond_wait? No one, because it's a thread-local variable. If it's
true before qemu_cond_wait, it will be true after qemu_cond_wait and you
don't need qemu_cond_wait_iothread... unless your compiler is broken and
doesn't generate TLS properly.
Can you compile cpus.c with -S and attach it?
Paolo
> qemu_tcg_cpu_thread_fn
> -> qemu_tcg_wait_io_event
> -> qemu_cond_wait acquires the mutex
>
> qemu_tcg_cpu_thread_fn
> -> tcg_exec_all -> tcg_cpu_exec -> cpu_exec
> -> cpu_exec ends up in calling prepare_mmio_access
- [Qemu-devel] [PATCH] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/24
- Re: [Qemu-devel] [PATCH] qemu_mutex_iothread_locked not correctly synchronized, Paolo Bonzini, 2015/11/24
- Re: [Qemu-devel] [PATCH] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/25
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/25
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, Paolo Bonzini, 2015/11/25
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/25
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/25
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, Paolo Bonzini, 2015/11/25
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/26
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, Stefan Weil, 2015/11/26
- Re: [Qemu-devel] [PATCH v2] qemu_mutex_iothread_locked not correctly synchronized, David Engraf, 2015/11/26