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Re: [Qemu-devel] [PATCH] fixup! block-migration: acquire AioContext as n
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH] fixup! block-migration: acquire AioContext as necessary |
Date: |
Tue, 23 Feb 2016 20:56:35 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, 02/23 10:42, Paolo Bonzini wrote:
>
>
> On 23/02/2016 06:39, Fam Zheng wrote:
> > BTW, could you also explain the blk_mig_lock() question (*) I had?
> >
> > *: https://lists.gnu.org/archive/html/qemu-devel/2016-02/msg03317.html
>
> Sorry, missed that:
>
> >
> >> @@ -597,21 +627,28 @@ static void block_migration_cleanup(void *opaque)
> >> {
> >> BlkMigDevState *bmds;
> >> BlkMigBlock *blk;
> >> + AioContext *ctx;
> >>
> >> bdrv_drain_all();
> >>
> >> unset_dirty_tracking();
> >>
> >> - blk_mig_lock();
> >
> > Why is it okay to skip the blk_mig_lock() for block_mig_state.bmds_list?
>
> The bmds_list is not protected by blk_mig_lock:
>
> /* Written during setup phase. Can be read without a lock. */
> int blk_enable;
> int shared_base;
> QSIMPLEQ_HEAD(bmds_list, BlkMigDevState) bmds_list;
> int64_t total_sector_sum;
> bool zero_blocks;
>
> block_migration_cleanup is called from qemu_savevm_state_cleanup, when
> there can be no concurrency between the migration thread and the I/O
> thread. In fact the call of qemu_savevm_state_cleanup might as well be
> moved out of the migration thread.
Thanks!
Fam