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Message-ID: <x49d0ebd2sl.fsf@segfault.boston.devel.redhat.com>
Date: Fri, 01 Nov 2019 11:39:06 -0400
From: Jeff Moyer <jmoyer@...hat.com>
To: Dan Carpenter <dan.carpenter@...cle.com>
Cc: Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] iocost: don't nest spin_lock_irq in ioc_weight_write()
Dan Carpenter <dan.carpenter@...cle.com> 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 <dan.carpenter@...cle.com>
> ---
> 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;
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