[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-block] [Qemu-devel] [PATCH v9 03/13] block/dirty-bitmap: add _

From: John Snow
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v9 03/13] block/dirty-bitmap: add _locked version of bdrv_reclaim_dirty_bitmap
Date: Wed, 24 Jan 2018 17:29:10 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 01/24/2018 05:16 AM, Paolo Bonzini wrote:
> On 22/01/2018 13:14, Vladimir Sementsov-Ogievskiy wrote:
>>> so, accessing the bitmap needs mutex lock?
>>> Then what do you mean under accessing the bitmap? Any touch of
>>> BdrvDirtyBitmap fields? Then "reading the list" will require bitmap
>>> mutex too.
>>> Or accessing the bitmap is accessing any field except
>>> BdrvDirtyBitmap.list? Then in (2), what do you mean? For example
>>> query-block will go through
>>> the list, but it touches other fields too, so it should lock mutex.
> The bitmap mutex is internal to block/dirty-bitmap.c.
>> and one more question:
>> What about qmp transactions? Should we lock mutex during the whole
>> transaction?
> Transactions hold the BQL, but you don't need to lock the bitmap mutex.
> Paolo

I would further add that attempting to lock all of the bitmap mutexes
during a transaction might cause complications if you try to perform two
actions on the same bitmap, and it deadlocks.

With the BQL held we're probably okay, but worst-case scenario locking
and unlocking per-each action is probably sufficient, I'd think.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]