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Re: [Qemu-block] [Qemu-devel] [PATCH 16/17] block: protect modification

From: Paolo Bonzini
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 16/17] block: protect modification of dirty bitmaps with a mutex
Date: Thu, 4 May 2017 12:05:23 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 04/05/2017 10:05, Fam Zheng wrote:
>>      /* Writing to the list requires the BQL _and_ the dirty_bitmap_mutex.
>>       * Reading from the list can be done with either the BQL or the
>> -     * dirty_bitmap_mutex.  Modifying a bitmap requires the AioContext
>> -     * lock.  */
>> +     * dirty_bitmap_mutex.  Modifying a bitmap only requires
>> +     * dirty_bitmap_mutex.  */
> I'm confused by this comment. What's added in this patch is bitmap->mutex, not
> dirty_bitmap_mutex. Is it a mistake?

bitmap->mutex is a pointer that points to the (single) per-BDS mutex.

This patch changes the modification of bitmaps to require bitmap->mutex
(which points to bs->dirty_bitmap_mutex) instead of the AioContext lock.


>>      QemuMutex dirty_bitmap_mutex;

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