QEMU-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Stefan Reiter <s.reiter@proxmox.com>
To: qemu-devel@nongnu.org, qemu-block@nongnu.org
Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, slp@redhat.com,
	mreitz@redhat.com, stefanha@redhat.com, jsnow@redhat.com,
	dietmar@proxmox.com
Subject: [PATCH v2 2/3] job: take each job's lock individually in job_txn_apply
Date: Thu, 26 Mar 2020 16:56:27 +0100
Message-ID: <20200326155628.859862-3-s.reiter@proxmox.com> (raw)
In-Reply-To: <20200326155628.859862-1-s.reiter@proxmox.com>

All callers of job_txn_apply hold a single job's lock, but different
jobs within a transaction can have different contexts, thus we need to
lock each one individually before applying the callback function.

Similar to job_completed_txn_abort this also requires releasing the
caller's context before and reacquiring it after to avoid recursive
locks which might break AIO_WAIT_WHILE in the callback.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
 job.c | 32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/job.c b/job.c
index 134a07b92e..e0966162fa 100644
--- a/job.c
+++ b/job.c
@@ -136,17 +136,33 @@ static void job_txn_del_job(Job *job)
     }
 }
 
-static int job_txn_apply(JobTxn *txn, int fn(Job *))
+static int job_txn_apply(Job *job, int fn(Job *))
 {
-    Job *job, *next;
+    AioContext *outer_ctx = job->aio_context;
+    AioContext *inner_ctx;
+    Job *other_job, *next;
+    JobTxn *txn = job->txn;
     int rc = 0;
 
-    QLIST_FOREACH_SAFE(job, &txn->jobs, txn_list, next) {
-        rc = fn(job);
+    /*
+     * Similar to job_completed_txn_abort, we take each job's lock before
+     * applying fn, but since we assume that outer_ctx is held by the caller,
+     * we need to release it here to avoid holding the lock twice - which would
+     * break AIO_WAIT_WHILE from within fn.
+     */
+    aio_context_release(outer_ctx);
+
+    QLIST_FOREACH_SAFE(other_job, &txn->jobs, txn_list, next) {
+        inner_ctx = other_job->aio_context;
+        aio_context_acquire(inner_ctx);
+        rc = fn(other_job);
+        aio_context_release(inner_ctx);
         if (rc) {
             break;
         }
     }
+
+    aio_context_acquire(outer_ctx);
     return rc;
 }
 
@@ -774,11 +790,11 @@ static void job_do_finalize(Job *job)
     assert(job && job->txn);
 
     /* prepare the transaction to complete */
-    rc = job_txn_apply(job->txn, job_prepare);
+    rc = job_txn_apply(job, job_prepare);
     if (rc) {
         job_completed_txn_abort(job);
     } else {
-        job_txn_apply(job->txn, job_finalize_single);
+        job_txn_apply(job, job_finalize_single);
     }
 }
 
@@ -824,10 +840,10 @@ static void job_completed_txn_success(Job *job)
         assert(other_job->ret == 0);
     }
 
-    job_txn_apply(txn, job_transition_to_pending);
+    job_txn_apply(job, job_transition_to_pending);
 
     /* If no jobs need manual finalization, automatically do so */
-    if (job_txn_apply(txn, job_needs_finalize) == 0) {
+    if (job_txn_apply(job, job_needs_finalize) == 0) {
         job_do_finalize(job);
     }
 }
-- 
2.26.0




  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-26 15:56 [PATCH v2 0/3] Fix some AIO context locking in jobs Stefan Reiter
2020-03-26 15:56 ` [PATCH v2 1/3] backup: don't acquire aio_context in backup_clean Stefan Reiter
2020-03-27  6:00   ` Vladimir Sementsov-Ogievskiy
2020-03-26 15:56 ` Stefan Reiter [this message]
2020-03-26 15:56 ` [PATCH v2 3/3] replication: acquire aio context before calling job_cancel_sync Stefan Reiter
2020-03-26 17:11 ` [PATCH v2 0/3] Fix some AIO context locking in jobs no-reply
2020-03-26 17:18 ` no-reply
2020-03-27  6:07 ` Dietmar Maurer
2020-03-27  6:13   ` Dietmar Maurer
2020-03-27  7:21   ` Dietmar Maurer
2020-03-27 10:00 ` Dietmar Maurer

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=20200326155628.859862-3-s.reiter@proxmox.com \
    --to=s.reiter@proxmox.com \
    --cc=dietmar@proxmox.com \
    --cc=jsnow@redhat.com \
    --cc=kwolf@redhat.com \
    --cc=mreitz@redhat.com \
    --cc=qemu-block@nongnu.org \
    --cc=qemu-devel@nongnu.org \
    --cc=slp@redhat.com \
    --cc=stefanha@redhat.com \
    --cc=vsementsov@virtuozzo.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

QEMU-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/qemu-devel/0 qemu-devel/git/0.git
	git clone --mirror https://lore.kernel.org/qemu-devel/1 qemu-devel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 qemu-devel qemu-devel/ https://lore.kernel.org/qemu-devel \
		qemu-devel@nongnu.org
	public-inbox-index qemu-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.nongnu.qemu-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git