[PATCH v2] bcache: explicitly destroy mutex while exiting

[PATCH v2] bcache: explicitly destroy mutex while exiting

[Liang Chen]

mutex_destroy does nothing most of time, but it's better to call
it to make the code future proof and it also has some meaning
for like mutex debug.

As Coly pointed out in a previous review, bcache_exit() may not be
able to handle all the references properly if userspace registers
cache and backing devices right before bch_debug_init runs and
bch_debug_init failes later. So not exposing userspace interface
until everything is ready to avoid that issue.

Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
---
 drivers/md/bcache/super.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index fc0a31b..25bf003 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -2085,6 +2085,7 @@ static void bcache_exit(void)
 	if (bcache_major)
 		unregister_blkdev(bcache_major, "bcache");
 	unregister_reboot_notifier(&reboot);
+	mutex_destroy(&bch_register_lock);
 }
 
 static int __init bcache_init(void)
@@ -2103,14 +2104,15 @@ static int __init bcache_init(void)
 	bcache_major = register_blkdev(0, "bcache");
 	if (bcache_major < 0) {
 		unregister_reboot_notifier(&reboot);
+		mutex_destroy(&bch_register_lock);
 		return bcache_major;
 	}
 
 	if (!(bcache_wq = alloc_workqueue("bcache", WQ_MEM_RECLAIM, 0)) ||
 	    !(bcache_kobj = kobject_create_and_add("bcache", fs_kobj)) ||
-	    sysfs_create_files(bcache_kobj, files) ||
 	    bch_request_init() ||
-	    bch_debug_init(bcache_kobj))
+	    bch_debug_init(bcache_kobj) ||
+	    sysfs_create_files(bcache_kobj, files))
 		goto err;
 
 	return 0;
-- 
1.8.3.1

Re: [PATCH v2] bcache: explicitly destroy mutex while exiting

[Coly Li]

On 2017/10/10 下午5:00, Liang Chen wrote:
> mutex_destroy does nothing most of time, but it's better to call
> it to make the code future proof and it also has some meaning
> for like mutex debug.
> 
> As Coly pointed out in a previous review, bcache_exit() may not be
> able to handle all the references properly if userspace registers
> cache and backing devices right before bch_debug_init runs and
> bch_debug_init failes later. So not exposing userspace interface
> until everything is ready to avoid that issue.
> 
> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>

Hi Liang,

No more comment from me, it looks good. Thanks.

Reviewed-by: Coly Li <colyli@suse.de>

> ---
>  drivers/md/bcache/super.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index fc0a31b..25bf003 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -2085,6 +2085,7 @@ static void bcache_exit(void)
>  	if (bcache_major)
>  		unregister_blkdev(bcache_major, "bcache");
>  	unregister_reboot_notifier(&reboot);
> +	mutex_destroy(&bch_register_lock);
>  }
>  
>  static int __init bcache_init(void)
> @@ -2103,14 +2104,15 @@ static int __init bcache_init(void)
>  	bcache_major = register_blkdev(0, "bcache");
>  	if (bcache_major < 0) {
>  		unregister_reboot_notifier(&reboot);
> +		mutex_destroy(&bch_register_lock);
>  		return bcache_major;
>  	}
>  
>  	if (!(bcache_wq = alloc_workqueue("bcache", WQ_MEM_RECLAIM, 0)) ||
>  	    !(bcache_kobj = kobject_create_and_add("bcache", fs_kobj)) ||
> -	    sysfs_create_files(bcache_kobj, files) ||
>  	    bch_request_init() ||
> -	    bch_debug_init(bcache_kobj))
> +	    bch_debug_init(bcache_kobj) ||
> +	    sysfs_create_files(bcache_kobj, files))
>  		goto err;
>  
>  	return 0;
> 


-- 
Coly Li

Re: [PATCH v2] bcache: explicitly destroy mutex while exiting

[Michael Lyle]

On 10/10/2017 05:25 AM, Coly Li wrote:
> On 2017/10/10 下午5:00, Liang Chen wrote:
>> mutex_destroy does nothing most of time, but it's better to call
>> it to make the code future proof and it also has some meaning
>> for like mutex debug.
>>
>> As Coly pointed out in a previous review, bcache_exit() may not be
>> able to handle all the references properly if userspace registers
>> cache and backing devices right before bch_debug_init runs and
>> bch_debug_init failes later. So not exposing userspace interface
>> until everything is ready to avoid that issue.
>>
>> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
> 
> Hi Liang,
> 
> No more comment from me, it looks good. Thanks.
> 
> Reviewed-by: Coly Li <colyli@suse.de>

Looks good to me too.

Reviewed-by: Michael Lyle <mlyle@lyle.org>

Re: [PATCH v2] bcache: explicitly destroy mutex while exiting

[Eric Wheeler]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1274 bytes --]

On Tue, 10 Oct 2017, Michael Lyle wrote:

> On 10/10/2017 05:25 AM, Coly Li wrote:
> > On 2017/10/10 下午5:00, Liang Chen wrote:
> >> mutex_destroy does nothing most of time, but it's better to call
> >> it to make the code future proof and it also has some meaning
> >> for like mutex debug.
> >>
> >> As Coly pointed out in a previous review, bcache_exit() may not be
> >> able to handle all the references properly if userspace registers
> >> cache and backing devices right before bch_debug_init runs and
> >> bch_debug_init failes later. So not exposing userspace interface
> >> until everything is ready to avoid that issue.
> >>
> >> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
> > 
> > Hi Liang,
> > 
> > No more comment from me, it looks good. Thanks.
> > 
> > Reviewed-by: Coly Li <colyli@suse.de>
> 
> Looks good to me too.
> 
> Reviewed-by: Michael Lyle <mlyle@lyle.org>

Should this Cc: stable to avoid the register race (possible 
crash?) described by Liang in other stable kernels?

Reviewed-by: Eric Wheeler <bcache@linux.ewheeler.net>

> 
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Re: [PATCH v2] bcache: explicitly destroy mutex while exiting

[Michael Lyle]

On Fri, Oct 27, 2017 at 12:05 PM, Eric Wheeler
<bcache@lists.ewheeler.net> wrote:
> Should this Cc: stable to avoid the register race (possible
> crash?) described by Liang in other stable kernels?
>
> Reviewed-by: Eric Wheeler <bcache@linux.ewheeler.net>

This seems like an unlikely failure; basically you must have built
bcache for debug (which not many of us are doing on previous stable
series), and then be critically out of resources at the time that
bcache is registering.  Seems like more trouble than it's worth to
send it to -stable.

Mike

Re: [PATCH v2] bcache: explicitly destroy mutex while exiting

[Liang C]

Hi Michael,
Would you please to include this patch in your tree for the next
release? It seems passed the review. Thank you.

Thanks,
Liang

On Tue, Oct 10, 2017 at 11:44 PM, Michael Lyle <mlyle@lyle.org> wrote:
> On 10/10/2017 05:25 AM, Coly Li wrote:
>> On 2017/10/10 下午5:00, Liang Chen wrote:
>>> mutex_destroy does nothing most of time, but it's better to call
>>> it to make the code future proof and it also has some meaning
>>> for like mutex debug.
>>>
>>> As Coly pointed out in a previous review, bcache_exit() may not be
>>> able to handle all the references properly if userspace registers
>>> cache and backing devices right before bch_debug_init runs and
>>> bch_debug_init failes later. So not exposing userspace interface
>>> until everything is ready to avoid that issue.
>>>
>>> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
>>
>> Hi Liang,
>>
>> No more comment from me, it looks good. Thanks.
>>
>> Reviewed-by: Coly Li <colyli@suse.de>
>
> Looks good to me too.
>
> Reviewed-by: Michael Lyle <mlyle@lyle.org>
>

Re: [PATCH v2] bcache: explicitly destroy mutex while exiting

[Michael Lyle]

Hi Liang--

On 10/30/2017 05:33 AM, Liang C wrote:
> Hi Michael,
> Would you please to include this patch in your tree for the next
> release? It seems passed the review. Thank you.
> 
> Thanks,
> Liang

Thanks for the reminder.

It's in my bcache-for-next tree at https://github.com/mlyle/linux/ along
with a few other small changes.  I am testing today and plan on sending
them up to Jens soon if I have good luck overall (and after reading
overall diff).

Though: it is getting late for non-critical changes in 4.15 so I need to
have perfect test sequences with no unexplained anomalies to send these
to Jens for 4.15.

Mike

> 
> On Tue, Oct 10, 2017 at 11:44 PM, Michael Lyle <mlyle@lyle.org> wrote:
>> On 10/10/2017 05:25 AM, Coly Li wrote:
>>> On 2017/10/10 下午5:00, Liang Chen wrote:
>>>> mutex_destroy does nothing most of time, but it's better to call
>>>> it to make the code future proof and it also has some meaning
>>>> for like mutex debug.
>>>>
>>>> As Coly pointed out in a previous review, bcache_exit() may not be
>>>> able to handle all the references properly if userspace registers
>>>> cache and backing devices right before bch_debug_init runs and
>>>> bch_debug_init failes later. So not exposing userspace interface
>>>> until everything is ready to avoid that issue.
>>>>
>>>> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
>>>
>>> Hi Liang,
>>>
>>> No more comment from me, it looks good. Thanks.
>>>
>>> Reviewed-by: Coly Li <colyli@suse.de>
>>
>> Looks good to me too.
>>
>> Reviewed-by: Michael Lyle <mlyle@lyle.org>
>>
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