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From: Paolo Bonzini <pbonzini@redhat.com>
To: "Emilio G. Cota" <cota@braap.org>
Cc: qemu-devel@nongnu.org, serge.fdrv@gmail.com,
	alex.bennee@linaro.org, sergey.fedorov@linaro.org
Subject: Re: [Qemu-devel] [PATCH 15/16] tcg: Make tb_flush() thread safe
Date: Wed, 21 Sep 2016 20:22:26 +0200	[thread overview]
Message-ID: <5d662563-6770-8ecb-8732-00e2f51ac484@redhat.com> (raw)
In-Reply-To: <20160921173726.GA27412@flamenco>



On 21/09/2016 19:37, Emilio G. Cota wrote:
> On Wed, Sep 21, 2016 at 18:19:26 +0200, Paolo Bonzini wrote:
>>
>>
>> On 21/09/2016 18:05, Emilio G. Cota wrote:
>>>>> +    tb_lock();
>>>>> +
>>>>> +    /* If it's already been done on request of another CPU,
>>>>> +     * just retry.
>>>>> +     */
>>>>> +    if (atomic_read(&tcg_ctx.tb_ctx.tb_flush_count) != tb_flush_req) {
>>>>> +        goto done;
>>> tb_flush_count is always accessed with tb_lock held, right? If so, I don't
>>> see a reason to access it with atomic_read/set.
>>
>> tb_flush accesses it outside tb_lock.  Technically this one you're
>> quoting need not use atomic_read, but others need to.
> 
> Sorry for being thick, but when does tb_flush not own tb_lock?
> (I'm assuming we're talking only user-mode, since full-system has
> for now empty tb_lock/unlock helpers.)

When called from gdbstub I think it doesn't (and for system-mode in
other cases too, so better be ready anyway).

Paolo

  reply	other threads:[~2016-09-21 18:22 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-19 12:50 [Qemu-devel] [PATCH v7 00/16] cpu-exec: Safe work in quiescent state Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 01/16] cpus: pass CPUState to run_on_cpu helpers Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 02/16] cpus: Move common code out of {async_, }run_on_cpu() Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 03/16] cpus: Rename flush_queued_work() Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 04/16] linux-user: Use QemuMutex and QemuCond Paolo Bonzini
2016-09-21 16:26   ` Emilio G. Cota
2016-09-21 16:32     ` Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 05/16] linux-user: Add qemu_cpu_is_self() and qemu_cpu_kick() Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 06/16] cpus-common: move CPU list management to common code Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 07/16] cpus-common: move CPU work item " Paolo Bonzini
2016-09-21 17:03   ` Emilio G. Cota
2016-09-21 17:15     ` Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 08/16] cpus-common: fix uninitialized variable use in run_on_cpu Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 09/16] cpus-common: move exclusive work infrastructure from linux-user Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 10/16] docs: include formal model for TCG exclusive sections Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 11/16] cpus-common: always defer async_run_on_cpu work items Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 12/16] cpus-common: remove redundant call to exclusive_idle() Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 13/16] cpus-common: simplify locking for start_exclusive/end_exclusive Paolo Bonzini
2016-09-21 16:15   ` Emilio G. Cota
2016-09-21 16:20     ` Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 14/16] cpus-common: Introduce async_safe_run_on_cpu() Paolo Bonzini
2016-09-21 16:08   ` Emilio G. Cota
2016-09-21 16:20     ` Paolo Bonzini
2016-09-19 12:50 ` [Qemu-devel] [PATCH 15/16] tcg: Make tb_flush() thread safe Paolo Bonzini
2016-09-21 16:05   ` Emilio G. Cota
2016-09-21 16:19     ` Paolo Bonzini
2016-09-21 17:37       ` Emilio G. Cota
2016-09-21 18:22         ` Paolo Bonzini [this message]
2016-09-19 12:50 ` [Qemu-devel] [PATCH 16/16] cpus-common: lock-free fast path for cpu_exec_start/end Paolo Bonzini
2016-09-21 17:24   ` Emilio G. Cota
2016-09-21 18:19     ` Paolo Bonzini
2016-09-21 22:14       ` Emilio G. Cota
2016-09-21 22:27   ` Emilio G. Cota
2016-09-22  8:46     ` Paolo Bonzini
2016-09-19 13:24 ` [Qemu-devel] [PATCH v7 00/16] cpu-exec: Safe work in quiescent state no-reply
2016-09-19 16:04 ` no-reply
2016-09-21 17:29 ` Emilio G. Cota
2016-09-21 18:20   ` Paolo Bonzini
  -- strict thread matches above, loose matches on Subject: below --
2016-09-23  7:31 [Qemu-devel] [PATCH v8 " Paolo Bonzini
2016-09-23  7:31 ` [Qemu-devel] [PATCH 15/16] tcg: Make tb_flush() thread safe Paolo Bonzini
2016-09-23 18:06   ` Richard Henderson
2016-09-24 11:51     ` Paolo Bonzini
2016-09-24 20:44       ` Richard Henderson
2016-09-26  7:24         ` Paolo Bonzini
2016-09-12 11:12 [Qemu-devel] [PATCH v7 00/16] cpu-exec: Safe work in quiescent state Paolo Bonzini
2016-09-12 11:12 ` [Qemu-devel] [PATCH 15/16] tcg: Make tb_flush() thread safe Paolo Bonzini

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