jobs: add job lock in find_* functions

Both blockdev.c and job-qmp.c have TOC/TOU conditions, because
they first search for the job and then perform an action on it.
Therefore, we need to do the search + action under the same
job mutex critical section.

Note: at this stage, job_{lock/unlock} and job lock guard macros
are *nop*.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20220926093214.506243-9-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -3313,9 +3313,13 @@ out:
     aio_context_release(aio_context);
 }
 
-/* Get a block job using its ID and acquire its AioContext */
-static BlockJob *find_block_job(const char *id, AioContext **aio_context,
-                                Error **errp)
+/*
+ * Get a block job using its ID and acquire its AioContext.
+ * Called with job_mutex held.
+ */
+static BlockJob *find_block_job_locked(const char *id,
+                                       AioContext **aio_context,
+                                       Error **errp)
 {
     BlockJob *job;
 
@@ -3323,7 +3327,7 @@ static BlockJob *find_block_job(const char *id, AioContext **aio_context,
 
     *aio_context = NULL;
 
-    job = block_job_get(id);
+    job = block_job_get_locked(id);
 
     if (!job) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
@@ -3340,13 +3344,16 @@ static BlockJob *find_block_job(const char *id, AioContext **aio_context,
 void qmp_block_job_set_speed(const char *device, int64_t speed, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job;
+
+    JOB_LOCK_GUARD();
+    job = find_block_job_locked(device, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
-    block_job_set_speed(job, speed, errp);
+    block_job_set_speed_locked(job, speed, errp);
     aio_context_release(aio_context);
 }
 
@@ -3354,7 +3361,10 @@ void qmp_block_job_cancel(const char *device,
                           bool has_force, bool force, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job;
+
+    JOB_LOCK_GUARD();
+    job = find_block_job_locked(device, &aio_context, errp);
 
     if (!job) {
         return;
@@ -3364,14 +3374,14 @@ void qmp_block_job_cancel(const char *device,
         force = false;
     }
 
-    if (job_user_paused(&job->job) && !force) {
+    if (job_user_paused_locked(&job->job) && !force) {
         error_setg(errp, "The block job for device '%s' is currently paused",
                    device);
         goto out;
     }
 
     trace_qmp_block_job_cancel(job);
-    job_user_cancel(&job->job, force, errp);
+    job_user_cancel_locked(&job->job, force, errp);
 out:
     aio_context_release(aio_context);
 }
@@ -3379,57 +3389,69 @@ out:
 void qmp_block_job_pause(const char *device, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job;
+
+    JOB_LOCK_GUARD();
+    job = find_block_job_locked(device, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_block_job_pause(job);
-    job_user_pause(&job->job, errp);
+    job_user_pause_locked(&job->job, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_block_job_resume(const char *device, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job;
+
+    JOB_LOCK_GUARD();
+    job = find_block_job_locked(device, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_block_job_resume(job);
-    job_user_resume(&job->job, errp);
+    job_user_resume_locked(&job->job, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_block_job_complete(const char *device, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *job = find_block_job(device, &aio_context, errp);
+    BlockJob *job;
+
+    JOB_LOCK_GUARD();
+    job = find_block_job_locked(device, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_block_job_complete(job);
-    job_complete(&job->job, errp);
+    job_complete_locked(&job->job, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_block_job_finalize(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *job = find_block_job(id, &aio_context, errp);
+    BlockJob *job;
+
+    JOB_LOCK_GUARD();
+    job = find_block_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_block_job_finalize(job);
-    job_ref(&job->job);
-    job_finalize(&job->job, errp);
+    job_ref_locked(&job->job);
+    job_finalize_locked(&job->job, errp);
 
     /*
      * Job's context might have changed via job_finalize (and job_txn_apply
@@ -3437,23 +3459,26 @@ void qmp_block_job_finalize(const char *id, Error **errp)
      * one.
      */
     aio_context = block_job_get_aio_context(job);
-    job_unref(&job->job);
+    job_unref_locked(&job->job);
     aio_context_release(aio_context);
 }
 
 void qmp_block_job_dismiss(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    BlockJob *bjob = find_block_job(id, &aio_context, errp);
+    BlockJob *bjob;
     Job *job;
 
+    JOB_LOCK_GUARD();
+    bjob = find_block_job_locked(id, &aio_context, errp);
+
     if (!bjob) {
         return;
     }
 
     trace_qmp_block_job_dismiss(bjob);
     job = &bjob->job;
-    job_dismiss(&job, errp);
+    job_dismiss_locked(&job, errp);
     aio_context_release(aio_context);
 }
 

job-qmp.c

@@ -29,14 +29,19 @@
 #include "qapi/error.h"
 #include "trace/trace-root.h"
 
-/* Get a job using its ID and acquire its AioContext */
-static Job *find_job(const char *id, AioContext **aio_context, Error **errp)
+/*
+ * Get a job using its ID and acquire its AioContext.
+ * Called with job_mutex held.
+ */
+static Job *find_job_locked(const char *id,
+                            AioContext **aio_context,
+                            Error **errp)
 {
     Job *job;
 
     *aio_context = NULL;
 
-    job = job_get(id);
+    job = job_get_locked(id);
     if (!job) {
         error_setg(errp, "Job not found");
         return NULL;
@@ -51,71 +56,86 @@ static Job *find_job(const char *id, AioContext **aio_context, Error **errp)
 void qmp_job_cancel(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job;
+
+    JOB_LOCK_GUARD();
+    job = find_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_job_cancel(job);
-    job_user_cancel(job, true, errp);
+    job_user_cancel_locked(job, true, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_job_pause(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job;
+
+    JOB_LOCK_GUARD();
+    job = find_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_job_pause(job);
-    job_user_pause(job, errp);
+    job_user_pause_locked(job, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_job_resume(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job;
+
+    JOB_LOCK_GUARD();
+    job = find_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_job_resume(job);
-    job_user_resume(job, errp);
+    job_user_resume_locked(job, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_job_complete(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job;
+
+    JOB_LOCK_GUARD();
+    job = find_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_job_complete(job);
-    job_complete(job, errp);
+    job_complete_locked(job, errp);
     aio_context_release(aio_context);
 }
 
 void qmp_job_finalize(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job;
+
+    JOB_LOCK_GUARD();
+    job = find_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_job_finalize(job);
-    job_ref(job);
-    job_finalize(job, errp);
+    job_ref_locked(job);
+    job_finalize_locked(job, errp);
 
     /*
      * Job's context might have changed via job_finalize (and job_txn_apply
@@ -123,21 +143,24 @@ void qmp_job_finalize(const char *id, Error **errp)
      * one.
      */
     aio_context = job->aio_context;
-    job_unref(job);
+    job_unref_locked(job);
     aio_context_release(aio_context);
 }
 
 void qmp_job_dismiss(const char *id, Error **errp)
 {
     AioContext *aio_context;
-    Job *job = find_job(id, &aio_context, errp);
+    Job *job;
+
+    JOB_LOCK_GUARD();
+    job = find_job_locked(id, &aio_context, errp);
 
     if (!job) {
         return;
     }
 
     trace_qmp_job_dismiss(job);
-    job_dismiss(&job, errp);
+    job_dismiss_locked(&job, errp);
     aio_context_release(aio_context);
 }