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Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitm
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex |
Date: |
Tue, 27 Jun 2017 11:27:42 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 |
On 27/06/2017 11:07, Vladimir Sementsov-Ogievskiy wrote:
> 26.06.2017 19:54, Paolo Bonzini wrote:
>>
>> On 26/06/2017 18:07, Vladimir Sementsov-Ogievskiy wrote:
>>> HI!
>>>
>>> One question here, should not 'bdrv_undo_clear_dirty_bitmap' be under
>>> lock too?
>> Any call to dirty bitmap functions between bdrv_clear_dirty_bitmap and
>> bdrv_undo_clear_dirty_bitmap is problematic anyway, so
>> bdrv_clear_dirty_bitmap really only needs the lock in the !out case;
>> bdrv_undo_clear_dirty_bitmap is only called when out != NULL.
>>
>> However, I agree it would be cleaner to add the lock there, too.
>
> Also, you've added comment "Called with BQL taken" both to functions
> that calls bdrv_dirty_bitmaps_lock and that do not... What is BQL?
It's the "big QEMU lock", also known as "iothread lock". The locking policy
is documented in block_int.h:
/* 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 only requires
* dirty_bitmap_mutex. */
QemuMutex dirty_bitmap_mutex;
QLIST_HEAD(, BdrvDirtyBitmap) dirty_bitmaps;
and the comments in block/dirty-bitmap.c reflect the above comment.
Paolo
- [Qemu-devel] [PATCH 08/19] throttle-groups: do not use qemu_co_enter_next, (continued)
- [Qemu-devel] [PATCH 08/19] throttle-groups: do not use qemu_co_enter_next, Paolo Bonzini, 2017/06/05
- [Qemu-devel] [PATCH 12/19] block: access write_gen with atomics, Paolo Bonzini, 2017/06/05
- [Qemu-devel] [PATCH 13/19] block: protect tracked_requests and flush_queue with reqs_lock, Paolo Bonzini, 2017/06/05
- [Qemu-devel] [PATCH 10/19] util: add stats64 module, Paolo Bonzini, 2017/06/05
- [Qemu-devel] [PATCH 14/19] block: introduce dirty_bitmap_mutex, Paolo Bonzini, 2017/06/05
- [Qemu-devel] [PATCH 17/19] block: introduce block_account_one_io, Paolo Bonzini, 2017/06/05
- [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Paolo Bonzini, 2017/06/05
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/26
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Paolo Bonzini, 2017/06/26
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Paolo Bonzini, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Paolo Bonzini, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Paolo Bonzini, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Paolo Bonzini, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27
- Re: [Qemu-devel] [PATCH 16/19] block: protect modification of dirty bitmaps with a mutex, Vladimir Sementsov-Ogievskiy, 2017/06/27