From: Stefan Reiter <s.reiter@proxmox.com>
To: Wolfgang Bumiller <w.bumiller@proxmox.com>
Cc: pve-devel@lists.proxmox.com
Subject: Re: [pve-devel] [PATCH qemu 2/2] PVE: Don't call job_cancel in coroutines
Date: Tue, 27 Oct 2020 15:57:06 +0100 [thread overview]
Message-ID: <9223e62b-4fee-3106-fe69-51d36a30e0b6@proxmox.com> (raw)
In-Reply-To: <20201027141734.x2puokunzh3nkww3@olga.proxmox.com>
On 10/27/20 3:17 PM, Wolfgang Bumiller wrote:
> On Thu, Oct 22, 2020 at 02:11:18PM +0200, Stefan Reiter wrote:
>> ...because it hangs on cancelling other jobs in the txn if you do.
>>
>> Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
>> ---
>> pve-backup.c | 26 +++++++++++++++++++++++++-
>> 1 file changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/pve-backup.c b/pve-backup.c
>> index 9179754dcb..af2db0d4b9 100644
>> --- a/pve-backup.c
>> +++ b/pve-backup.c
>> @@ -82,6 +82,12 @@ typedef struct PVEBackupDevInfo {
>> BlockJob *job;
>> } PVEBackupDevInfo;
>>
>> +typedef struct JobCancelData {
>> + AioContext *ctx;
>> + Coroutine *co;
>> + Job *job;
>> +} JobCancelData;
>> +
>> static void pvebackup_propagate_error(Error *err)
>> {
>> qemu_mutex_lock(&backup_state.stat.lock);
>> @@ -332,6 +338,18 @@ static void pvebackup_complete_cb(void *opaque, int ret)
>> aio_co_enter(qemu_get_aio_context(), co);
>> }
>>
>> +/*
>> + * job_cancel(_sync) does not like to be called from coroutines, so defer to
>> + * main loop processing via a bottom half.
>> + */
>> +static void job_cancel_bh(void *opaque) {
>> + JobCancelData *data = (JobCancelData*)opaque;
>> + aio_context_acquire(data->job->aio_context);
>> + job_cancel_sync(data->job);
>> + aio_context_release(data->job->aio_context);
>> + aio_co_schedule(data->ctx, data->co);
>> +}
>> +
>> static void coroutine_fn pvebackup_co_cancel(void *opaque)
>> {
>> Error *cancel_err = NULL;
>> @@ -357,7 +375,13 @@ static void coroutine_fn pvebackup_co_cancel(void *opaque)
>> NULL;
>>
>> if (cancel_job) {
>> - job_cancel(&cancel_job->job, false);
>> + JobCancelData data = {
>> + .ctx = qemu_get_current_aio_context(),
>> + .co = qemu_coroutine_self(),
>> + .job = &cancel_job->job,
>> + };
>> + aio_bh_schedule_oneshot(data.ctx, job_cancel_bh, &data);
>> + qemu_coroutine_yield();
>
> Don't we need some kind of synchronization here? The yield does not
> guarantee we don't run before the bh is run, or does it? Maybe a condvar
> to trigger the coro after the job cancel bh?
>
No, it cannot race, since we execute the BH in the same context as the
coroutine (qemu_get_current_aio_context()). The coroutine thus blocks
execution of the BH until it yields.
See also code and comment in aio_co_reschedule_self() from 'util/async.c'.
>> }
>>
>> qemu_co_mutex_unlock(&backup_state.backup_mutex);
>> --
>> 2.20.1
next prev parent reply other threads:[~2020-10-27 14:57 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 12:11 [pve-devel] [PATCH 0/2] QEMU backup cancellation fixes Stefan Reiter
2020-10-22 12:11 ` [pve-devel] [PATCH qemu 1/2] PVE: Don't expect complete_cb to be called outside coroutine Stefan Reiter
2020-10-27 14:16 ` Wolfgang Bumiller
2020-10-27 14:57 ` Stefan Reiter
2020-10-22 12:11 ` [pve-devel] [PATCH qemu 2/2] PVE: Don't call job_cancel in coroutines Stefan Reiter
2020-10-27 14:17 ` Wolfgang Bumiller
2020-10-27 14:57 ` Stefan Reiter [this message]
2020-10-22 13:07 ` [pve-devel] [PATCH 0/2] QEMU backup cancellation fixes Dominik Csapak
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9223e62b-4fee-3106-fe69-51d36a30e0b6@proxmox.com \
--to=s.reiter@proxmox.com \
--cc=pve-devel@lists.proxmox.com \
--cc=w.bumiller@proxmox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox