2019-10-31 10:55:19

by Dan Carpenter

Subject: [PATCH] iocost: don't nest spin_lock_irq in ioc_weight_write()

This code causes a static analysis warning:

block/blk-iocost.c:2113 ioc_weight_write() error: double lock 'irq'

We disable IRQs in blkg_conf_prep() and re-enable them in
blkg_conf_finish(). IRQ disable/enable should not be nested because
that means the IRQs will be enabled at the first unlock instead of the
second one.

Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
Signed-off-by: Dan Carpenter <[email protected]>
---
block/blk-iocost.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 2a3db80c1dce..a7ed434eae03 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2110,10 +2110,10 @@ static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
goto einval;
}

- spin_lock_irq(&iocg->ioc->lock);
+ spin_lock(&iocg->ioc->lock);
iocg->cfg_weight = v;
weight_updated(iocg);
- spin_unlock_irq(&iocg->ioc->lock);
+ spin_unlock(&iocg->ioc->lock);

blkg_conf_finish(&ctx);
return nbytes;
--
2.20.1

2019-10-31 16:51:25

by Tejun Heo

Subject: Re: [PATCH] iocost: don't nest spin_lock_irq in ioc_weight_write()

On Thu, Oct 31, 2019 at 01:53:41PM +0300, Dan Carpenter wrote:
> This code causes a static analysis warning:
>
> block/blk-iocost.c:2113 ioc_weight_write() error: double lock 'irq'
>
> We disable IRQs in blkg_conf_prep() and re-enable them in
> blkg_conf_finish(). IRQ disable/enable should not be nested because
> that means the IRQs will be enabled at the first unlock instead of the
> second one.
>
> Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
> Signed-off-by: Dan Carpenter <[email protected]>

Acked-by: Tejun Heo <[email protected]>

Thanks.

--
tejun

2019-10-31 21:47:40

by Jens Axboe

Subject: Re: [PATCH] iocost: don't nest spin_lock_irq in ioc_weight_write()

On 10/31/19 4:53 AM, Dan Carpenter wrote:
> This code causes a static analysis warning:
>
> block/blk-iocost.c:2113 ioc_weight_write() error: double lock 'irq'
>
> We disable IRQs in blkg_conf_prep() and re-enable them in
> blkg_conf_finish(). IRQ disable/enable should not be nested because
> that means the IRQs will be enabled at the first unlock instead of the
> second one.

Applied for 5.3, thanks.

--
Jens Axboe

2019-11-01 16:04:23

by Jeff Moyer

Subject: Re: [PATCH] iocost: don't nest spin_lock_irq in ioc_weight_write()

Dan Carpenter <[email protected]> writes:

> This code causes a static analysis warning:
>
> block/blk-iocost.c:2113 ioc_weight_write() error: double lock 'irq'
>
> We disable IRQs in blkg_conf_prep() and re-enable them in
> blkg_conf_finish(). IRQ disable/enable should not be nested because
> that means the IRQs will be enabled at the first unlock instead of the
> second one.

Can you please also add a comment stating that irqs were disabled in
blkg_conf_prep? Otherwise future readers will surely be scratching
their heads trying to figure out why we do things two different ways in
the same function.

Thanks!
Jeff

>
> Fixes: 7caa47151ab2 ("blkcg: implement blk-iocost")
> Signed-off-by: Dan Carpenter <[email protected]>
> ---
> block/blk-iocost.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index 2a3db80c1dce..a7ed434eae03 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -2110,10 +2110,10 @@ static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
> goto einval;
> }
>
> - spin_lock_irq(&iocg->ioc->lock);
> + spin_lock(&iocg->ioc->lock);
> iocg->cfg_weight = v;
> weight_updated(iocg);
> - spin_unlock_irq(&iocg->ioc->lock);
> + spin_unlock(&iocg->ioc->lock);
>
> blkg_conf_finish(&ctx);
> return nbytes;

2019-11-04 10:19:34

by Dan Carpenter

Subject: [PATCH] iocost: add a comment about locking in ioc_weight_write()

It wasn't very clear that blkg_conf_prep() disables IRQ and that they
are enabled in blkg_conf_finish() so this patch adds a comment about it.

Signed-off-by: Dan Carpenter <[email protected]>
---
I don't know if it's too late to fold this in with the previous patch?

block/blk-iocost.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index a7ed434eae03..c5a8703ca6aa 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2095,6 +2095,7 @@ static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
return nbytes;
}

+ /* blkg_conf_prep() takes the q->queue_lock and disables IRQs */
ret = blkg_conf_prep(blkcg, &blkcg_policy_iocost, buf, &ctx);
if (ret)
return ret;
@@ -2115,6 +2116,7 @@ static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
weight_updated(iocg);
spin_unlock(&iocg->ioc->lock);

+ /* blkg_conf_finish() unlocks the q->queue_lock and enables IRQs */
blkg_conf_finish(&ctx);
return nbytes;

--
2.20.1

2019-11-04 12:00:40

by Jeff Moyer

Subject: Re: [PATCH] iocost: add a comment about locking in ioc_weight_write()

Dan Carpenter <[email protected]> writes:

> It wasn't very clear that blkg_conf_prep() disables IRQ and that they
> are enabled in blkg_conf_finish() so this patch adds a comment about it.
>
> Signed-off-by: Dan Carpenter <[email protected]>

Reviewed-by: Jeff Moyer <[email protected]>

Thanks, Dan!

> ---
> I don't know if it's too late to fold this in with the previous patch?
>
> block/blk-iocost.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index a7ed434eae03..c5a8703ca6aa 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -2095,6 +2095,7 @@ static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
> return nbytes;
> }
>
> + /* blkg_conf_prep() takes the q->queue_lock and disables IRQs */
> ret = blkg_conf_prep(blkcg, &blkcg_policy_iocost, buf, &ctx);
> if (ret)
> return ret;
> @@ -2115,6 +2116,7 @@ static ssize_t ioc_weight_write(struct kernfs_open_file *of, char *buf,
> weight_updated(iocg);
> spin_unlock(&iocg->ioc->lock);
>
> + /* blkg_conf_finish() unlocks the q->queue_lock and enables IRQs */
> blkg_conf_finish(&ctx);
> return nbytes;