blockjob: add pause points
Block jobs are coroutines that usually perform I/O but sometimes also sleep or yield. Currently only sleeping or yielded block jobs can be paused. This means jobs that do not sleep or yield (using block_job_yield()) are unaffected by block_job_pause(). Add block_job_pause_point() so that block jobs can mark quiescent points that are suitable for pausing. This solves the problem that it can take a block job a long time to pause if it is performing a long series of I/O operations. Transitioning to paused state involves a .pause()/.resume() callback. These callbacks are used to ensure that I/O and event loop activity has ceased while the job is at a pause point. Note that this patch introduces a stricter pause state than previously. The job->busy flag was incorrectly documented as a quiescent state without I/O pending. This is violated by any job that has I/O pending across sleep or block_job_yield(), like the mirror block job. [Add missing block_job_should_pause() check to avoid deadlock after job->driver->pause() in block_job_pause_point(). --Stefan] Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Message-id: 1466096189-6477-4-git-send-email-stefanha@redhat.com
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blockjob.c
38
blockjob.c
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@ -257,6 +257,32 @@ static bool block_job_should_pause(BlockJob *job)
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return job->pause_count > 0;
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return job->pause_count > 0;
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}
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}
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void coroutine_fn block_job_pause_point(BlockJob *job)
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{
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if (!block_job_should_pause(job)) {
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return;
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}
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if (block_job_is_cancelled(job)) {
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return;
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}
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if (job->driver->pause) {
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job->driver->pause(job);
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}
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if (block_job_should_pause(job) && !block_job_is_cancelled(job)) {
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job->paused = true;
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job->busy = false;
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qemu_coroutine_yield(); /* wait for block_job_resume() */
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job->busy = true;
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job->paused = false;
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}
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if (job->driver->resume) {
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job->driver->resume(job);
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}
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}
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void block_job_resume(BlockJob *job)
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void block_job_resume(BlockJob *job)
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{
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{
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assert(job->pause_count > 0);
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assert(job->pause_count > 0);
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@ -364,11 +390,9 @@ void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns)
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if (!block_job_should_pause(job)) {
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if (!block_job_should_pause(job)) {
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co_aio_sleep_ns(blk_get_aio_context(job->blk), type, ns);
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co_aio_sleep_ns(blk_get_aio_context(job->blk), type, ns);
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}
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}
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/* The job can be paused while sleeping, so check this again */
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if (block_job_should_pause(job)) {
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qemu_coroutine_yield();
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}
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job->busy = true;
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job->busy = true;
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block_job_pause_point(job);
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}
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}
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void block_job_yield(BlockJob *job)
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void block_job_yield(BlockJob *job)
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@ -381,8 +405,12 @@ void block_job_yield(BlockJob *job)
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}
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}
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job->busy = false;
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job->busy = false;
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qemu_coroutine_yield();
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if (!block_job_should_pause(job)) {
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qemu_coroutine_yield();
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}
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job->busy = true;
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job->busy = true;
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block_job_pause_point(job);
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}
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}
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BlockJobInfo *block_job_query(BlockJob *job)
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BlockJobInfo *block_job_query(BlockJob *job)
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@ -70,6 +70,20 @@ typedef struct BlockJobDriver {
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* never both.
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* never both.
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*/
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*/
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void (*abort)(BlockJob *job);
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void (*abort)(BlockJob *job);
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/**
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* If the callback is not NULL, it will be invoked when the job transitions
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* into the paused state. Paused jobs must not perform any asynchronous
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* I/O or event loop activity. This callback is used to quiesce jobs.
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*/
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void coroutine_fn (*pause)(BlockJob *job);
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/**
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* If the callback is not NULL, it will be invoked when the job transitions
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* out of the paused state. Any asynchronous I/O or event loop activity
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* should be restarted from this callback.
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*/
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void coroutine_fn (*resume)(BlockJob *job);
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} BlockJobDriver;
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} BlockJobDriver;
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/**
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/**
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@ -119,12 +133,18 @@ struct BlockJob {
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bool user_paused;
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bool user_paused;
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/**
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/**
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* Set to false by the job while it is in a quiescent state, where
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* Set to false by the job while the coroutine has yielded and may be
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* no I/O is pending and the job has yielded on any condition
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* re-entered by block_job_enter(). There may still be I/O or event loop
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* that is not detected by #aio_poll, such as a timer.
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* activity pending.
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*/
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*/
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bool busy;
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bool busy;
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/**
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* Set to true by the job while it is in a quiescent state, where
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* no I/O or event loop activity is pending.
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*/
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bool paused;
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/**
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/**
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* Set to true when the job is ready to be completed.
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* Set to true when the job is ready to be completed.
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*/
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*/
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@ -298,6 +318,15 @@ bool block_job_is_cancelled(BlockJob *job);
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*/
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*/
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BlockJobInfo *block_job_query(BlockJob *job);
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BlockJobInfo *block_job_query(BlockJob *job);
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/**
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* block_job_pause_point:
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* @job: The job that is ready to pause.
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*
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* Pause now if block_job_pause() has been called. Block jobs that perform
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* lots of I/O must call this between requests so that the job can be paused.
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*/
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void coroutine_fn block_job_pause_point(BlockJob *job);
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/**
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/**
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* block_job_pause:
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* block_job_pause:
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* @job: The job to be paused.
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* @job: The job to be paused.
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