From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <fam@euphon.net>,
qemu-devel@nongnu.org, Hanna Reitz <hreitz@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
John Snow <jsnow@redhat.com>
Subject: Re: [PATCH 10/12] block.c: add subtree_drains where needed
Date: Thu, 3 Feb 2022 11:09:14 +0100 [thread overview]
Message-ID: <74cd9429-c15c-713d-4e9b-ae6e7a212500@redhat.com> (raw)
In-Reply-To: <fbc50950-5124-87a2-a876-6e22e5a10404@redhat.com>
On 02/02/2022 18:38, Paolo Bonzini wrote:
> On 2/2/22 16:37, Emanuele Giuseppe Esposito wrote:
>> So we have disk B with backing file C, and new disk A that wants to have
>> backing file C.
>>
>> I think I understand what you mean, so in theory the operation would be
>> - create new child
>> - add child to A->children list
>> - add child to C->parents list
>>
>> So in theory we need to
>> * drain A (without subtree), because it can't happen that child nodes of
>> A have in-flight requests that look at A status (children list),
>> right?
>> In other words, if A has another node X, can a request in X inspect
>> A->children
I am not sure if this can happen. It doesn't seem so, though. All
functions inspecting ->parents are either GS or don't call recursive
function that go down on children list again.
>> * drain C, as parents can inspect C status (like B). Same assumption
>> here, C->children[x]->bs cannot have requests inspecting C->parents
>> list?
What if C->children[x]->bs drains? we would have a child inspecting
C->parents.
>
> In that case (i.e. if parents have to be drained, but children need not)
> bdrv_drained_begin_unlocked would be enough, right?
Should be, if that is the case.
>
> That would mean that ->children is I/O state but ->parents is global
> state. I think it's quite a bit more complicated to analyze and to
> understand.
Not sure I follow this one, why is ->parents GS? it is also used by the
drain API...
Emanuele
next prev parent reply other threads:[~2022-02-03 10:10 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-18 16:27 [PATCH 00/12] Removal of Aiocontext lock through drains: protect bdrv_replace_child_noperm Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 01/12] introduce BDRV_POLL_WHILE_UNLOCKED Emanuele Giuseppe Esposito
2022-01-26 10:49 ` Stefan Hajnoczi
2022-02-03 13:57 ` Emanuele Giuseppe Esposito
2022-02-04 12:13 ` Paolo Bonzini
2022-01-18 16:27 ` [PATCH 02/12] block/io.c: make bdrv_do_drained_begin_quiesce static and introduce bdrv_drained_begin_no_poll Emanuele Giuseppe Esposito
2022-01-19 9:11 ` Paolo Bonzini
2022-01-18 16:27 ` [PATCH 03/12] block.c: bdrv_replace_child_noperm: first remove the child, and then call ->detach() Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 04/12] block.c: bdrv_replace_child_noperm: first call ->attach(), and then add child Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 05/12] test-bdrv-drain.c: adapt test to the coming subtree drains Emanuele Giuseppe Esposito
2022-01-19 9:18 ` Paolo Bonzini
2022-02-03 11:41 ` Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 06/12] test-bdrv-drain.c: remove test_detach_by_parent_cb() Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 07/12] block/io.c: introduce bdrv_subtree_drained_{begin/end}_unlocked Emanuele Giuseppe Esposito
2022-01-19 9:52 ` Paolo Bonzini
2022-01-26 11:04 ` Stefan Hajnoczi
2022-01-18 16:27 ` [PATCH 08/12] reopen: add a transaction to drain_end nodes picked in bdrv_reopen_parse_file_or_backing Emanuele Giuseppe Esposito
2022-01-19 9:33 ` Paolo Bonzini
2022-01-26 11:16 ` Stefan Hajnoczi
2022-01-18 16:27 ` [PATCH 09/12] jobs: ensure sleep in job_sleep_ns is fully performed Emanuele Giuseppe Esposito
2022-01-26 11:21 ` Stefan Hajnoczi
2022-02-03 14:21 ` Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 10/12] block.c: add subtree_drains where needed Emanuele Giuseppe Esposito
2022-01-19 9:47 ` Paolo Bonzini
2022-02-03 13:13 ` Emanuele Giuseppe Esposito
2022-02-01 14:47 ` Vladimir Sementsov-Ogievskiy
2022-02-02 15:37 ` Emanuele Giuseppe Esposito
2022-02-02 17:38 ` Paolo Bonzini
2022-02-03 10:09 ` Emanuele Giuseppe Esposito [this message]
2022-02-04 9:49 ` Vladimir Sementsov-Ogievskiy
2022-02-04 13:30 ` Emanuele Giuseppe Esposito
2022-02-04 14:03 ` Vladimir Sementsov-Ogievskiy
2022-01-18 16:27 ` [PATCH 11/12] block/io.c: fully enable assert_bdrv_graph_writable Emanuele Giuseppe Esposito
2022-01-18 16:27 ` [PATCH 12/12] block.c: additional assert qemu in main tread Emanuele Giuseppe Esposito
2022-01-19 9:51 ` [PATCH 00/12] Removal of Aiocontext lock through drains: protect bdrv_replace_child_noperm Paolo Bonzini
2022-01-26 11:29 ` Stefan Hajnoczi
2022-01-27 13:46 ` Paolo Bonzini
2022-01-28 12:20 ` Emanuele Giuseppe Esposito
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