In message: Re: [linux-yocto][linux-yocto v5.15/standard/base][PATCH 1/1]
mtd_blkdevs: add mtd_table_mutex lock back to blktrans_{open, release} to avoid
race condition
on 09/09/2022 Paul Gortmaker wrote:
> [[linux-yocto][linux-yocto v5.15/standard/base][PATCH 1/1] mtd_blkdevs: add
> mtd_table_mutex lock back to blktrans_{open, release} to avoid race
> condition] On 09/09/2022 (Fri 16:26) LiweiSong wrote:
>
> > without lock mtd_table_mutex in blktrans_{open, release}, there will
> > be a race condition when access devices /dev/mtd1 and /dev/mtdblock1
> > at the same time with a high frequency open and close test:
> >
> > kernel BUG at drivers/mtd/mtdcore.c:1221!
> > Internal error: Oops - BUG: 0 1 PREEMPT_RT SMP
> > CPU: 0 PID: 15349 Comm: mtd-test Not tainted 5.15.52-rt41-yocto-preempt-rt
> > #1
> > Hardware name: SoCFPGA Stratix 10 SoCDK (DT)
> > pstate: 60000005put_mtd_device+0x4c/0x84
> > lr : blktrans_release+0xb0/0x120
> > Call trace:
> > __put_mtd_device+0x4c/0x84
> > blktrans_release+0xb0/0x120
> > blkdev_put+0xd4/0x210
> > blkdev_close+0x34/0x50
> > __fput+0x8c/0x240
> > ____fput+0x1c/0x30
> > task_work_run+0x98/00t_64_sync_handler+0xa4/0x130
> > el0t_64_sync+0x1a0/0x1a4
>
> In the interest of transparency - ongoing discussions continue on how
> best to fix this in mainline - albeit slowly.
>
> https://lore.kernel.org/all/cf66e306-f216-5247-7cff-36ce08eb4...@windriver.com/
>
> So even while this may not be the eventual mainline solution, the
> thought here is that it is a viable temporary one that resolves the
> failing test case(s) for Yocto and has no known negative side effects.
Thanks Paul! You saved me digging around for why this was coming
from a staging branch.
I agree with the analysis and have merged the change.
Bruce
>
> Thanks,
> Paul.
> --
>
> >
> > since the original purpose of commit 799ae31c58ae ("mtd_blkdevs:
> > don't hold del_mtd_blktrans_dev in blktrans_{open, release}") is
> > to fix a DEADLOCK issue, here convert mutex_lock to mutex_trylock
> > and return immediately if failed acquire mtd_table_mutex, then
> > both race condition and DEADLOCK can be avoided.
> >
> > Fixes: 799ae31c58ae ("mtd_blkdevs: don't hold del_mtd_blktrans_dev in
> > blktrans_{open, release}")
> > Signed-off-by: Liwei Song <liwei.s...@windriver.com>
> > ---
> > drivers/mtd/mtd_blkdevs.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> > index b8ae1ec14e17..147e4a11dfe4 100644
> > --- a/drivers/mtd/mtd_blkdevs.c
> > +++ b/drivers/mtd/mtd_blkdevs.c
> > @@ -188,6 +188,8 @@ static int blktrans_open(struct block_device *bdev,
> > fmode_t mode)
> >
> > kref_get(&dev->ref);
> >
> > + if (!mutex_trylock(&mtd_table_mutex))
> > + return ret;
> > mutex_lock(&dev->lock);
> >
> > if (dev->open)
> > @@ -212,6 +214,7 @@ static int blktrans_open(struct block_device *bdev,
> > fmode_t mode)
> > unlock:
> > dev->open++;
> > mutex_unlock(&dev->lock);
> > + mutex_unlock(&mtd_table_mutex);
> > return ret;
> >
> > error_release:
> > @@ -220,6 +223,7 @@ static int blktrans_open(struct block_device *bdev,
> > fmode_t mode)
> > error_put:
> > module_put(dev->tr->owner);
> > mutex_unlock(&dev->lock);
> > + mutex_unlock(&mtd_table_mutex);
> > blktrans_dev_put(dev);
> > return ret;
> > }
> > @@ -228,6 +232,8 @@ static void blktrans_release(struct gendisk *disk,
> > fmode_t mode)
> > {
> > struct mtd_blktrans_dev *dev = disk->private_data;
> >
> > + if (!mutex_trylock(&mtd_table_mutex))
> > + return;
> > mutex_lock(&dev->lock);
> >
> > if (--dev->open)
> > @@ -242,6 +248,7 @@ static void blktrans_release(struct gendisk *disk,
> > fmode_t mode)
> > }
> > unlock:
> > mutex_unlock(&dev->lock);
> > + mutex_unlock(&mtd_table_mutex);
> > blktrans_dev_put(dev);
> > }
> >
> > --
> > 2.36.1
> >
>
> >
> >
> >
>
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