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From 01dd04dfd1421d041da935e7a22987d0883b4353 Mon Sep 17 00:00:00 2001
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From: Jeffrey Cody <jcody@redhat.com>
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Date: Thu, 30 Nov 2017 22:49:07 +0100
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Subject: [PATCH 03/21] blockjob: do not allow coroutine double entry or
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entry-after-completion
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RH-Author: Jeffrey Cody <jcody@redhat.com>
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Message-id: <36a71db70d56ebdb223c760e682a146ad91d97ad.1511985875.git.jcody@redhat.com>
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Patchwork-id: 78041
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O-Subject: [RHV7.5 qemu-kvm-rhev PATCH 03/11] blockjob: do not allow coroutine double entry or entry-after-completion
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Bugzilla: 1506531
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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When block_job_sleep_ns() is called, the co-routine is scheduled for
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future execution. If we allow the job to be re-entered prior to the
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scheduled time, we present a race condition in which a coroutine can be
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entered recursively, or even entered after the coroutine is deleted.
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The job->busy flag is used by blockjobs when a coroutine is busy
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executing. The function 'block_job_enter()' obeys the busy flag,
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and will not enter a coroutine if set. If we sleep a job, we need to
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leave the busy flag set, so that subsequent calls to block_job_enter()
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are prevented.
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This changes the prior behavior of block_job_cancel() being able to
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immediately wake up and cancel a job; in practice, this should not be an
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issue, as the coroutine sleep times are generally very small, and the
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cancel will occur the next time the coroutine wakes up.
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This fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1508708
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit 4afeffc8572f40d8844b946a30c00b10da4442b1)
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Signed-off-by: Jeff Cody <jcody@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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blockjob.c | 7 +++++--
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include/block/blockjob_int.h | 3 ++-
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2 files changed, 7 insertions(+), 3 deletions(-)
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diff --git a/blockjob.c b/blockjob.c
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index 70a7818..c3cf9a2 100644
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--- a/blockjob.c
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+++ b/blockjob.c
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@@ -797,11 +797,14 @@ void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns)
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return;
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}
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- job->busy = false;
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+ /* We need to leave job->busy set here, because when we have
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+ * put a coroutine to 'sleep', we have scheduled it to run in
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+ * the future. We cannot enter that same coroutine again before
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+ * it wakes and runs, otherwise we risk double-entry or entry after
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+ * completion. */
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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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}
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- job->busy = true;
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block_job_pause_point(job);
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}
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diff --git a/include/block/blockjob_int.h b/include/block/blockjob_int.h
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index f13ad05..43f3be2 100644
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--- a/include/block/blockjob_int.h
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+++ b/include/block/blockjob_int.h
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@@ -143,7 +143,8 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
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* @ns: How many nanoseconds to stop for.
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*
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* Put the job to sleep (assuming that it wasn't canceled) for @ns
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- * nanoseconds. Canceling the job will interrupt the wait immediately.
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+ * nanoseconds. Canceling the job will not interrupt the wait, so the
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+ * cancel will not process until the coroutine wakes up.
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*/
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void block_job_sleep_ns(BlockJob *job, QEMUClockType type, int64_t ns);
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--
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1.8.3.1
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