Re: [RFC PATCH 2/6] job: _locked functions and public job_lock/unlock for next patch
On Mon, Jul 12, 2021 at 10:43:07AM +0200, Emanuele Giuseppe Esposito wrote:
>
>
> On 08/07/2021 12:50, Stefan Hajnoczi wrote:
> > On Wed, Jul 07, 2021 at 06:58:09PM +0200, Emanuele Giuseppe Esposito wrote:
> > > diff --git a/job.c b/job.c
> > > index 872bbebb01..96fb8e9730 100644
> > > --- a/job.c
> > > +++ b/job.c
> > > @@ -32,6 +32,10 @@
> > > #include "trace/trace-root.h"
> > > #include "qapi/qapi-events-job.h"
> > > +/* job_mutex protexts the jobs list, but also the job operations. */
> > > +static QemuMutex job_mutex;
> >
> > It's unclear what protecting "job operations" means. I would prefer a
> > fine-grained per-job lock that protects the job's fields instead of a
> > global lock with an unclear scope.
>
> As I wrote in the cover letter, I wanted to try to keep things as simple as
> possible with a global lock. It is possible to try and have a per-job lock,
> but I don't know how complex will that be then.
> I will try and see what I can do.
>
> Maybe "job_mutex protexts the jobs list, but also makes the job API
> thread-safe"?
That's clearer, thanks. I thought "job operations" meant the processing
that the actual block jobs do (commit, mirror, stream, backup).
>
> >
> > > +
> > > +/* Protected by job_mutex */
> > > static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
> > > /* Job State Transition Table */
> > > @@ -64,27 +68,22 @@ bool JobVerbTable[JOB_VERB__MAX][JOB_STATUS__MAX] = {
> > > /* Transactional group of jobs */
> > > struct JobTxn {
> > > -/* Is this txn being cancelled? */
> > > +/* Is this txn being cancelled? Atomic.*/
> > > bool aborting;
> >
> > The comment says atomic but this field is not accessed using atomic
> > operations (at least at this point in the patch series)?
>
> Yes sorry I messed up the hunks in one-two patches. These comments were
> supposed to be on patch 4 "job.h: categorize job fields". Even though that
> might also not be ideal, since that patch just introduces the comments,
> without applying the locking/protection yet.
> On the other side, if I merge everything together in patch 5, it will be
> even harder to read.
The commit description can describe changes that currently have no
effect but are anticipating a later patch. That helps reviewers
understand whether the change is intentional/correct.
Stefan
signature.asc
Description: PGP signature
Re: [RFC PATCH 2/6] job: _locked functions and public job_lock/unlock for next patch
On 08/07/2021 12:50, Stefan Hajnoczi wrote:
On Wed, Jul 07, 2021 at 06:58:09PM +0200, Emanuele Giuseppe Esposito wrote:
diff --git a/job.c b/job.c
index 872bbebb01..96fb8e9730 100644
--- a/job.c
+++ b/job.c
@@ -32,6 +32,10 @@
#include "trace/trace-root.h"
#include "qapi/qapi-events-job.h"
+/* job_mutex protexts the jobs list, but also the job operations. */
+static QemuMutex job_mutex;
It's unclear what protecting "job operations" means. I would prefer a
fine-grained per-job lock that protects the job's fields instead of a
global lock with an unclear scope.
As I wrote in the cover letter, I wanted to try to keep things as simple
as possible with a global lock. It is possible to try and have a per-job
lock, but I don't know how complex will that be then.
I will try and see what I can do.
Maybe "job_mutex protexts the jobs list, but also makes the job API
thread-safe"?
+
+/* Protected by job_mutex */
static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
/* Job State Transition Table */
@@ -64,27 +68,22 @@ bool JobVerbTable[JOB_VERB__MAX][JOB_STATUS__MAX] = {
/* Transactional group of jobs */
struct JobTxn {
-/* Is this txn being cancelled? */
+/* Is this txn being cancelled? Atomic.*/
bool aborting;
The comment says atomic but this field is not accessed using atomic
operations (at least at this point in the patch series)?
Yes sorry I messed up the hunks in one-two patches. These comments were
supposed to be on patch 4 "job.h: categorize job fields". Even though
that might also not be ideal, since that patch just introduces the
comments, without applying the locking/protection yet.
On the other side, if I merge everything together in patch 5, it will be
even harder to read.
Emanuele
-/* List of jobs */
+/* List of jobs. Protected by job_mutex. */
QLIST_HEAD(, Job) jobs;
-/* Reference count */
+/* Reference count. Atomic. */
int refcnt;
Same.
Re: [RFC PATCH 2/6] job: _locked functions and public job_lock/unlock for next patch
On Wed, Jul 07, 2021 at 06:58:09PM +0200, Emanuele Giuseppe Esposito wrote:
> diff --git a/job.c b/job.c
> index 872bbebb01..96fb8e9730 100644
> --- a/job.c
> +++ b/job.c
> @@ -32,6 +32,10 @@
> #include "trace/trace-root.h"
> #include "qapi/qapi-events-job.h"
>
> +/* job_mutex protexts the jobs list, but also the job operations. */
> +static QemuMutex job_mutex;
It's unclear what protecting "job operations" means. I would prefer a
fine-grained per-job lock that protects the job's fields instead of a
global lock with an unclear scope.
> +
> +/* Protected by job_mutex */
> static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
>
> /* Job State Transition Table */
> @@ -64,27 +68,22 @@ bool JobVerbTable[JOB_VERB__MAX][JOB_STATUS__MAX] = {
> /* Transactional group of jobs */
> struct JobTxn {
>
> -/* Is this txn being cancelled? */
> +/* Is this txn being cancelled? Atomic.*/
> bool aborting;
The comment says atomic but this field is not accessed using atomic
operations (at least at this point in the patch series)?
>
> -/* List of jobs */
> +/* List of jobs. Protected by job_mutex. */
> QLIST_HEAD(, Job) jobs;
>
> -/* Reference count */
> +/* Reference count. Atomic. */
> int refcnt;
Same.
signature.asc
Description: PGP signature
[RFC PATCH 2/6] job: _locked functions and public job_lock/unlock for next patch
Create _locked functions, to make next patch a little bit smaller.
Also set the locking functions as public, so that they can be used
also from structures using the Job struct.
Signed-off-by: Emanuele Giuseppe Esposito
---
include/qemu/job.h | 23 +
job.c | 85 ++
2 files changed, 93 insertions(+), 15 deletions(-)
diff --git a/include/qemu/job.h b/include/qemu/job.h
index 72c7d0f69d..ba2f9b2660 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -305,6 +305,7 @@ void job_txn_add_job(JobTxn *txn, Job *job);
/** Returns the @ret field of a given Job. */
int job_get_ret(Job *job);
+int job_get_ret_locked(Job *job);
/** Returns the AioContext of a given Job. */
AioContext *job_get_aiocontext(Job *job);
@@ -336,6 +337,24 @@ bool job_is_force_cancel(Job *job);
/** Returns the statis of a given Job. */
JobStatus job_get_status(Job *job);
+/**
+ * job_lock:
+ *
+ * Take the mutex protecting the list of jobs and their status.
+ * Most functions called by the monitor need to call job_lock
+ * and job_unlock manually. On the other hand, function called
+ * by the block jobs themselves and by the block layer will take the
+ * lock for you.
+ */
+void job_lock(void);
+
+/**
+ * job_unlock:
+ *
+ * Release the mutex protecting the list of jobs and their status.
+ */
+void job_unlock(void);
+
/**
* Create a new long-running job and return it.
*
@@ -424,6 +443,7 @@ void job_start(Job *job);
* Continue the specified job by entering the coroutine.
*/
void job_enter(Job *job);
+void job_enter_locked(Job *job);
/**
* @job: The job that is ready to pause.
@@ -462,12 +482,15 @@ bool job_is_internal(Job *job);
/** Returns whether the job is scheduled for cancellation. */
bool job_is_cancelled(Job *job);
+bool job_is_cancelled_locked(Job *job);
/** Returns whether the job is in a completed state. */
bool job_is_completed(Job *job);
+bool job_is_completed_locked(Job *job);
/** Returns whether the job is ready to be completed. */
bool job_is_ready(Job *job);
+bool job_is_ready_locked(Job *job);
/**
* Request @job to pause at the next pause point. Must be paired with
diff --git a/job.c b/job.c
index 872bbebb01..96fb8e9730 100644
--- a/job.c
+++ b/job.c
@@ -32,6 +32,10 @@
#include "trace/trace-root.h"
#include "qapi/qapi-events-job.h"
+/* job_mutex protexts the jobs list, but also the job operations. */
+static QemuMutex job_mutex;
+
+/* Protected by job_mutex */
static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
/* Job State Transition Table */
@@ -64,27 +68,22 @@ bool JobVerbTable[JOB_VERB__MAX][JOB_STATUS__MAX] = {
/* Transactional group of jobs */
struct JobTxn {
-/* Is this txn being cancelled? */
+/* Is this txn being cancelled? Atomic.*/
bool aborting;
-/* List of jobs */
+/* List of jobs. Protected by job_mutex. */
QLIST_HEAD(, Job) jobs;
-/* Reference count */
+/* Reference count. Atomic. */
int refcnt;
};
-/* Right now, this mutex is only needed to synchronize accesses to job->busy
- * and job->sleep_timer, such as concurrent calls to job_do_yield and
- * job_enter. */
-static QemuMutex job_mutex;
-
-static void job_lock(void)
+void job_lock(void)
{
qemu_mutex_lock(_mutex);
}
-static void job_unlock(void)
+void job_unlock(void)
{
qemu_mutex_unlock(_mutex);
}
@@ -109,11 +108,22 @@ bool job_is_busy(Job *job)
return qatomic_read(>busy);
}
-int job_get_ret(Job *job)
+/* Called with job_mutex held. */
+int job_get_ret_locked(Job *job)
{
return job->ret;
}
+/* Called with job_mutex *not* held. */
+int job_get_ret(Job *job)
+{
+int ret;
+job_lock();
+ret = job_get_ret_locked(job);
+job_unlock();
+return ret;
+}
+
Error *job_get_err(Job *job)
{
return job->err;
@@ -255,12 +265,24 @@ const char *job_type_str(const Job *job)
return JobType_str(job_type(job));
}
-bool job_is_cancelled(Job *job)
+/* Called with job_mutex held. */
+bool job_is_cancelled_locked(Job *job)
{
return job->cancelled;
}
-bool job_is_ready(Job *job)
+/* Called with job_mutex *not* held. */
+bool job_is_cancelled(Job *job)
+{
+bool ret;
+job_lock();
+ret = job_is_cancelled_locked(job);
+job_unlock();
+return ret;
+}
+
+/* Called with job_mutex held. */
+bool job_is_ready_locked(Job *job)
{
switch (job->status) {
case JOB_STATUS_UNDEFINED:
@@ -282,7 +304,18 @@ bool job_is_ready(Job *job)
return false;
}
-bool job_is_completed(Job *job)
+/* Called with job_mutex *not* held. */
+bool job_is_ready(Job *job)
+{
+bool ret;
+job_lock();
+ret = job_is_ready_locked(job);
+job_unlock();
+return ret;
+}
+
+/* Called with job_mutex held. */
+bool job_is_completed_locked(Job *job)
{
switch (job->status) {
case JOB_STATUS_UNDEFINED:
@@ -304,6 +337,17 @@ bool job_is_completed(Job *job)
return false;
}
+/* Called with job_mutex *not*
