[PATCH v2] mtd: break circular locks in register_mtd_blktrans

[PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

Syzbot reported a circular locking dependency:
https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb

This happens because of the following lock dependencies:

1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
loop_remove, which then calls del_gendisk; this also happens in
loop_exit which eventually calls loop_remove)

2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
__blkdev_get, which then calls blktrans_open)

3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
calls __register_blkdev)

4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
loop_probe)

Hence there's an overall dependency of:

loop_ctl_mutex   ----------> bdev->bd_mutex
      ^                            |
      |                            |
      |                            v
major_names_lock <---------  mtd_table_mutex

We can break this circular dependency by holding mtd_table_mutex only
for the required critical section in register_mtd_blktrans. This
avoids the mtd_table_mutex -> major_names_lock dependency.

Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
Co-developed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---

Changes in v1 -> v2:

Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.

 drivers/mtd/mtd_blkdevs.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..7d26cfe24d05 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	if (!blktrans_notifier.list.next)
 		register_mtd_user(&blktrans_notifier);
 
-
-	mutex_lock(&mtd_table_mutex);
-
 	ret = register_blkdev(tr->major, tr->name);
 	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
-		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
@@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);
-	list_add(&tr->list, &blktrans_majors);
 
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
 		if (mtd->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd);
-
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }
-- 
2.25.1

[PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

Syzbot reported a circular locking dependency:
https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb

This happens because of the following lock dependencies:

1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
loop_remove, which then calls del_gendisk; this also happens in
loop_exit which eventually calls loop_remove)

2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
__blkdev_get, which then calls blktrans_open)

3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
calls __register_blkdev)

4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
loop_probe)

Hence there's an overall dependency of:

loop_ctl_mutex   ----------> bdev->bd_mutex
      ^                            |
      |                            |
      |                            v
major_names_lock <---------  mtd_table_mutex

We can break this circular dependency by holding mtd_table_mutex only
for the required critical section in register_mtd_blktrans. This
avoids the mtd_table_mutex -> major_names_lock dependency.

Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
Co-developed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---

Changes in v1 -> v2:

Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.

 drivers/mtd/mtd_blkdevs.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..7d26cfe24d05 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	if (!blktrans_notifier.list.next)
 		register_mtd_user(&blktrans_notifier);
 
-
-	mutex_lock(&mtd_table_mutex);
-
 	ret = register_blkdev(tr->major, tr->name);
 	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
-		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
@@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);
-	list_add(&tr->list, &blktrans_majors);
 
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
 		if (mtd->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd);
-
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }
-- 
2.25.1


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

[PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

Syzbot reported a circular locking dependency:
https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb

This happens because of the following lock dependencies:

1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
loop_remove, which then calls del_gendisk; this also happens in
loop_exit which eventually calls loop_remove)

2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
__blkdev_get, which then calls blktrans_open)

3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
calls __register_blkdev)

4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
loop_probe)

Hence there's an overall dependency of:

loop_ctl_mutex   ----------> bdev->bd_mutex
      ^                            |
      |                            |
      |                            v
major_names_lock <---------  mtd_table_mutex

We can break this circular dependency by holding mtd_table_mutex only
for the required critical section in register_mtd_blktrans. This
avoids the mtd_table_mutex -> major_names_lock dependency.

Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
Co-developed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---

Changes in v1 -> v2:

Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.

 drivers/mtd/mtd_blkdevs.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index fb8e12d590a1..7d26cfe24d05 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	if (!blktrans_notifier.list.next)
 		register_mtd_user(&blktrans_notifier);
 
-
-	mutex_lock(&mtd_table_mutex);
-
 	ret = register_blkdev(tr->major, tr->name);
 	if (ret < 0) {
 		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
 		       tr->name, tr->major, ret);
-		mutex_unlock(&mtd_table_mutex);
 		return ret;
 	}
 
@@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	tr->blkshift = ffs(tr->blksize) - 1;
 
 	INIT_LIST_HEAD(&tr->devs);
-	list_add(&tr->list, &blktrans_majors);
 
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
 		if (mtd->type != MTD_ABSENT)
 			tr->add_mtd(tr, mtd);
-
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }
-- 
2.25.1

_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
> Syzbot reported a circular locking dependency:
> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> 
> This happens because of the following lock dependencies:
> 
> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> loop_remove, which then calls del_gendisk; this also happens in
> loop_exit which eventually calls loop_remove)
> 
> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> __blkdev_get, which then calls blktrans_open)
> 
> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> calls __register_blkdev)
> 
> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> loop_probe)
> 
> Hence there's an overall dependency of:
> 
> loop_ctl_mutex   ----------> bdev->bd_mutex
>        ^                            |
>        |                            |
>        |                            v
> major_names_lock <---------  mtd_table_mutex
> 
> We can break this circular dependency by holding mtd_table_mutex only
> for the required critical section in register_mtd_blktrans. This
> avoids the mtd_table_mutex -> major_names_lock dependency.
> 
> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> Co-developed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> ---
> 
> Changes in v1 -> v2:
> 
> Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
> 
>   drivers/mtd/mtd_blkdevs.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> index fb8e12d590a1..7d26cfe24d05 100644
> --- a/drivers/mtd/mtd_blkdevs.c
> +++ b/drivers/mtd/mtd_blkdevs.c
> @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>   	if (!blktrans_notifier.list.next)
>   		register_mtd_user(&blktrans_notifier);
>   
> -
> -	mutex_lock(&mtd_table_mutex);
> -
>   	ret = register_blkdev(tr->major, tr->name);
>   	if (ret < 0) {
>   		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
>   		       tr->name, tr->major, ret);
> -		mutex_unlock(&mtd_table_mutex);
>   		return ret;
>   	}
>   
> @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>   	tr->blkshift = ffs(tr->blksize) - 1;
>   
>   	INIT_LIST_HEAD(&tr->devs);
> -	list_add(&tr->list, &blktrans_majors);
>   
> +	mutex_lock(&mtd_table_mutex);
> +	list_add(&tr->list, &blktrans_majors);
>   	mtd_for_each_device(mtd)
>   		if (mtd->type != MTD_ABSENT)
>   			tr->add_mtd(tr, mtd);
> -
>   	mutex_unlock(&mtd_table_mutex);
>   	return 0;
>   }
> 

Hi maintainers,

Any chance to review this patch?

For additional reference, the mtd_table_mutex --> major_names_lock 
hierarchy that can be removed by this patch also appears in a different 
lock chain:
https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750

Best wishes,
Desmond

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
> Syzbot reported a circular locking dependency:
> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> 
> This happens because of the following lock dependencies:
> 
> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> loop_remove, which then calls del_gendisk; this also happens in
> loop_exit which eventually calls loop_remove)
> 
> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> __blkdev_get, which then calls blktrans_open)
> 
> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> calls __register_blkdev)
> 
> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> loop_probe)
> 
> Hence there's an overall dependency of:
> 
> loop_ctl_mutex   ----------> bdev->bd_mutex
>        ^                            |
>        |                            |
>        |                            v
> major_names_lock <---------  mtd_table_mutex
> 
> We can break this circular dependency by holding mtd_table_mutex only
> for the required critical section in register_mtd_blktrans. This
> avoids the mtd_table_mutex -> major_names_lock dependency.
> 
> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> Co-developed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> ---
> 
> Changes in v1 -> v2:
> 
> Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
> 
>   drivers/mtd/mtd_blkdevs.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> index fb8e12d590a1..7d26cfe24d05 100644
> --- a/drivers/mtd/mtd_blkdevs.c
> +++ b/drivers/mtd/mtd_blkdevs.c
> @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>   	if (!blktrans_notifier.list.next)
>   		register_mtd_user(&blktrans_notifier);
>   
> -
> -	mutex_lock(&mtd_table_mutex);
> -
>   	ret = register_blkdev(tr->major, tr->name);
>   	if (ret < 0) {
>   		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
>   		       tr->name, tr->major, ret);
> -		mutex_unlock(&mtd_table_mutex);
>   		return ret;
>   	}
>   
> @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>   	tr->blkshift = ffs(tr->blksize) - 1;
>   
>   	INIT_LIST_HEAD(&tr->devs);
> -	list_add(&tr->list, &blktrans_majors);
>   
> +	mutex_lock(&mtd_table_mutex);
> +	list_add(&tr->list, &blktrans_majors);
>   	mtd_for_each_device(mtd)
>   		if (mtd->type != MTD_ABSENT)
>   			tr->add_mtd(tr, mtd);
> -
>   	mutex_unlock(&mtd_table_mutex);
>   	return 0;
>   }
> 

Hi maintainers,

Any chance to review this patch?

For additional reference, the mtd_table_mutex --> major_names_lock 
hierarchy that can be removed by this patch also appears in a different 
lock chain:
https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750

Best wishes,
Desmond

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
> Syzbot reported a circular locking dependency:
> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> 
> This happens because of the following lock dependencies:
> 
> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> loop_remove, which then calls del_gendisk; this also happens in
> loop_exit which eventually calls loop_remove)
> 
> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> __blkdev_get, which then calls blktrans_open)
> 
> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> calls __register_blkdev)
> 
> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> loop_probe)
> 
> Hence there's an overall dependency of:
> 
> loop_ctl_mutex   ----------> bdev->bd_mutex
>        ^                            |
>        |                            |
>        |                            v
> major_names_lock <---------  mtd_table_mutex
> 
> We can break this circular dependency by holding mtd_table_mutex only
> for the required critical section in register_mtd_blktrans. This
> avoids the mtd_table_mutex -> major_names_lock dependency.
> 
> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> Co-developed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> ---
> 
> Changes in v1 -> v2:
> 
> Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
> 
>   drivers/mtd/mtd_blkdevs.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> index fb8e12d590a1..7d26cfe24d05 100644
> --- a/drivers/mtd/mtd_blkdevs.c
> +++ b/drivers/mtd/mtd_blkdevs.c
> @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>   	if (!blktrans_notifier.list.next)
>   		register_mtd_user(&blktrans_notifier);
>   
> -
> -	mutex_lock(&mtd_table_mutex);
> -
>   	ret = register_blkdev(tr->major, tr->name);
>   	if (ret < 0) {
>   		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
>   		       tr->name, tr->major, ret);
> -		mutex_unlock(&mtd_table_mutex);
>   		return ret;
>   	}
>   
> @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>   	tr->blkshift = ffs(tr->blksize) - 1;
>   
>   	INIT_LIST_HEAD(&tr->devs);
> -	list_add(&tr->list, &blktrans_majors);
>   
> +	mutex_lock(&mtd_table_mutex);
> +	list_add(&tr->list, &blktrans_majors);
>   	mtd_for_each_device(mtd)
>   		if (mtd->type != MTD_ABSENT)
>   			tr->add_mtd(tr, mtd);
> -
>   	mutex_unlock(&mtd_table_mutex);
>   	return 0;
>   }
> 

Hi maintainers,

Any chance to review this patch?

For additional reference, the mtd_table_mutex --> major_names_lock 
hierarchy that can be removed by this patch also appears in a different 
lock chain:
https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750

Best wishes,
Desmond
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Miquel Raynal]

Hello,

Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote on Wed, 30 Jun
2021 16:04:17 +0800:

> On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
> > Syzbot reported a circular locking dependency:
> > https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> > 
> > This happens because of the following lock dependencies:
> > 
> > 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> > loop_remove, which then calls del_gendisk; this also happens in
> > loop_exit which eventually calls loop_remove)
> > 
> > 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> > __blkdev_get, which then calls blktrans_open)
> > 
> > 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> > calls __register_blkdev)
> > 
> > 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> > loop_probe)
> > 
> > Hence there's an overall dependency of:
> > 
> > loop_ctl_mutex   ----------> bdev->bd_mutex
> >        ^                            |
> >        |                            |
> >        |                            v
> > major_names_lock <---------  mtd_table_mutex
> > 
> > We can break this circular dependency by holding mtd_table_mutex only
> > for the required critical section in register_mtd_blktrans. This
> > avoids the mtd_table_mutex -> major_names_lock dependency.
> > 
> > Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> > Co-developed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> > ---
> > 
> > Changes in v1 -> v2:
> > 
> > Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
> > 
> >   drivers/mtd/mtd_blkdevs.c | 8 ++------
> >   1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> > index fb8e12d590a1..7d26cfe24d05 100644
> > --- a/drivers/mtd/mtd_blkdevs.c
> > +++ b/drivers/mtd/mtd_blkdevs.c
> > @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
> >   	if (!blktrans_notifier.list.next)
> >   		register_mtd_user(&blktrans_notifier);
> >   > -
> > -	mutex_lock(&mtd_table_mutex);
> > -
> >   	ret = register_blkdev(tr->major, tr->name);
> >   	if (ret < 0) {
> >   		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
> >   		       tr->name, tr->major, ret);
> > -		mutex_unlock(&mtd_table_mutex);
> >   		return ret;
> >   	}
> >   > @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
> >   	tr->blkshift = ffs(tr->blksize) - 1;
> >   >   	INIT_LIST_HEAD(&tr->devs);
> > -	list_add(&tr->list, &blktrans_majors);
> >   > +	mutex_lock(&mtd_table_mutex);
> > +	list_add(&tr->list, &blktrans_majors);
> >   	mtd_for_each_device(mtd)
> >   		if (mtd->type != MTD_ABSENT)
> >   			tr->add_mtd(tr, mtd);
> > -
> >   	mutex_unlock(&mtd_table_mutex);
> >   	return 0;
> >   }
> > 
> 
> Hi maintainers,
> 
> Any chance to review this patch?
> 
> For additional reference, the mtd_table_mutex --> major_names_lock hierarchy that can be removed by this patch also appears in a different lock chain:
> https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750

I'm fine with the patch, but it came too late in the release cycle so
now I'm waiting -rc1 to apply it.

Thanks,
Miquèl

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Miquel Raynal]

Hello,

Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote on Wed, 30 Jun
2021 16:04:17 +0800:

> On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
> > Syzbot reported a circular locking dependency:
> > https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> > 
> > This happens because of the following lock dependencies:
> > 
> > 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> > loop_remove, which then calls del_gendisk; this also happens in
> > loop_exit which eventually calls loop_remove)
> > 
> > 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> > __blkdev_get, which then calls blktrans_open)
> > 
> > 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> > calls __register_blkdev)
> > 
> > 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> > loop_probe)
> > 
> > Hence there's an overall dependency of:
> > 
> > loop_ctl_mutex   ----------> bdev->bd_mutex
> >        ^                            |
> >        |                            |
> >        |                            v
> > major_names_lock <---------  mtd_table_mutex
> > 
> > We can break this circular dependency by holding mtd_table_mutex only
> > for the required critical section in register_mtd_blktrans. This
> > avoids the mtd_table_mutex -> major_names_lock dependency.
> > 
> > Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> > Co-developed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> > ---
> > 
> > Changes in v1 -> v2:
> > 
> > Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
> > 
> >   drivers/mtd/mtd_blkdevs.c | 8 ++------
> >   1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> > index fb8e12d590a1..7d26cfe24d05 100644
> > --- a/drivers/mtd/mtd_blkdevs.c
> > +++ b/drivers/mtd/mtd_blkdevs.c
> > @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
> >   	if (!blktrans_notifier.list.next)
> >   		register_mtd_user(&blktrans_notifier);
> >   > -
> > -	mutex_lock(&mtd_table_mutex);
> > -
> >   	ret = register_blkdev(tr->major, tr->name);
> >   	if (ret < 0) {
> >   		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
> >   		       tr->name, tr->major, ret);
> > -		mutex_unlock(&mtd_table_mutex);
> >   		return ret;
> >   	}
> >   > @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
> >   	tr->blkshift = ffs(tr->blksize) - 1;
> >   >   	INIT_LIST_HEAD(&tr->devs);
> > -	list_add(&tr->list, &blktrans_majors);
> >   > +	mutex_lock(&mtd_table_mutex);
> > +	list_add(&tr->list, &blktrans_majors);
> >   	mtd_for_each_device(mtd)
> >   		if (mtd->type != MTD_ABSENT)
> >   			tr->add_mtd(tr, mtd);
> > -
> >   	mutex_unlock(&mtd_table_mutex);
> >   	return 0;
> >   }
> > 
> 
> Hi maintainers,
> 
> Any chance to review this patch?
> 
> For additional reference, the mtd_table_mutex --> major_names_lock hierarchy that can be removed by this patch also appears in a different lock chain:
> https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750

I'm fine with the patch, but it came too late in the release cycle so
now I'm waiting -rc1 to apply it.

Thanks,
Miquèl

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Miquel Raynal]

Hello,

Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote on Wed, 30 Jun
2021 16:04:17 +0800:

> On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
> > Syzbot reported a circular locking dependency:
> > https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> > 
> > This happens because of the following lock dependencies:
> > 
> > 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> > loop_remove, which then calls del_gendisk; this also happens in
> > loop_exit which eventually calls loop_remove)
> > 
> > 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> > __blkdev_get, which then calls blktrans_open)
> > 
> > 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> > calls __register_blkdev)
> > 
> > 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> > loop_probe)
> > 
> > Hence there's an overall dependency of:
> > 
> > loop_ctl_mutex   ----------> bdev->bd_mutex
> >        ^                            |
> >        |                            |
> >        |                            v
> > major_names_lock <---------  mtd_table_mutex
> > 
> > We can break this circular dependency by holding mtd_table_mutex only
> > for the required critical section in register_mtd_blktrans. This
> > avoids the mtd_table_mutex -> major_names_lock dependency.
> > 
> > Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> > Co-developed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> > ---
> > 
> > Changes in v1 -> v2:
> > 
> > Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
> > 
> >   drivers/mtd/mtd_blkdevs.c | 8 ++------
> >   1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
> > index fb8e12d590a1..7d26cfe24d05 100644
> > --- a/drivers/mtd/mtd_blkdevs.c
> > +++ b/drivers/mtd/mtd_blkdevs.c
> > @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
> >   	if (!blktrans_notifier.list.next)
> >   		register_mtd_user(&blktrans_notifier);
> >   > -
> > -	mutex_lock(&mtd_table_mutex);
> > -
> >   	ret = register_blkdev(tr->major, tr->name);
> >   	if (ret < 0) {
> >   		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
> >   		       tr->name, tr->major, ret);
> > -		mutex_unlock(&mtd_table_mutex);
> >   		return ret;
> >   	}
> >   > @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
> >   	tr->blkshift = ffs(tr->blksize) - 1;
> >   >   	INIT_LIST_HEAD(&tr->devs);
> > -	list_add(&tr->list, &blktrans_majors);
> >   > +	mutex_lock(&mtd_table_mutex);
> > +	list_add(&tr->list, &blktrans_majors);
> >   	mtd_for_each_device(mtd)
> >   		if (mtd->type != MTD_ABSENT)
> >   			tr->add_mtd(tr, mtd);
> > -
> >   	mutex_unlock(&mtd_table_mutex);
> >   	return 0;
> >   }
> > 
> 
> Hi maintainers,
> 
> Any chance to review this patch?
> 
> For additional reference, the mtd_table_mutex --> major_names_lock hierarchy that can be removed by this patch also appears in a different lock chain:
> https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750

I'm fine with the patch, but it came too late in the release cycle so
now I'm waiting -rc1 to apply it.

Thanks,
Miquèl
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

On 30/6/21 4:43 pm, Miquel Raynal wrote:
> Hello,
> 
> Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote on Wed, 30 Jun
> 2021 16:04:17 +0800:
> 
>> On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
>>> Syzbot reported a circular locking dependency:
>>> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
>>>
>>> This happens because of the following lock dependencies:
>>>
>>> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
>>> loop_remove, which then calls del_gendisk; this also happens in
>>> loop_exit which eventually calls loop_remove)
>>>
>>> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
>>> __blkdev_get, which then calls blktrans_open)
>>>
>>> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
>>> calls __register_blkdev)
>>>
>>> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
>>> loop_probe)
>>>
>>> Hence there's an overall dependency of:
>>>
>>> loop_ctl_mutex   ----------> bdev->bd_mutex
>>>         ^                            |
>>>         |                            |
>>>         |                            v
>>> major_names_lock <---------  mtd_table_mutex
>>>
>>> We can break this circular dependency by holding mtd_table_mutex only
>>> for the required critical section in register_mtd_blktrans. This
>>> avoids the mtd_table_mutex -> major_names_lock dependency.
>>>
>>> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
>>> Co-developed-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
>>> ---
>>>
>>> Changes in v1 -> v2:
>>>
>>> Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
>>>
>>>    drivers/mtd/mtd_blkdevs.c | 8 ++------
>>>    1 file changed, 2 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
>>> index fb8e12d590a1..7d26cfe24d05 100644
>>> --- a/drivers/mtd/mtd_blkdevs.c
>>> +++ b/drivers/mtd/mtd_blkdevs.c
>>> @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>>>    	if (!blktrans_notifier.list.next)
>>>    		register_mtd_user(&blktrans_notifier);
>>>    > -
>>> -	mutex_lock(&mtd_table_mutex);
>>> -
>>>    	ret = register_blkdev(tr->major, tr->name);
>>>    	if (ret < 0) {
>>>    		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
>>>    		       tr->name, tr->major, ret);
>>> -		mutex_unlock(&mtd_table_mutex);
>>>    		return ret;
>>>    	}
>>>    > @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>>>    	tr->blkshift = ffs(tr->blksize) - 1;
>>>    >   	INIT_LIST_HEAD(&tr->devs);
>>> -	list_add(&tr->list, &blktrans_majors);
>>>    > +	mutex_lock(&mtd_table_mutex);
>>> +	list_add(&tr->list, &blktrans_majors);
>>>    	mtd_for_each_device(mtd)
>>>    		if (mtd->type != MTD_ABSENT)
>>>    			tr->add_mtd(tr, mtd);
>>> -
>>>    	mutex_unlock(&mtd_table_mutex);
>>>    	return 0;
>>>    }
>>>
>>
>> Hi maintainers,
>>
>> Any chance to review this patch?
>>
>> For additional reference, the mtd_table_mutex --> major_names_lock hierarchy that can be removed by this patch also appears in a different lock chain:
>> https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750
> 
> I'm fine with the patch, but it came too late in the release cycle so
> now I'm waiting -rc1 to apply it.
> 
> Thanks,
> Miquèl
> 

Got it. Thanks for the review, Miquèl.

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

On 30/6/21 4:43 pm, Miquel Raynal wrote:
> Hello,
> 
> Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote on Wed, 30 Jun
> 2021 16:04:17 +0800:
> 
>> On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
>>> Syzbot reported a circular locking dependency:
>>> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
>>>
>>> This happens because of the following lock dependencies:
>>>
>>> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
>>> loop_remove, which then calls del_gendisk; this also happens in
>>> loop_exit which eventually calls loop_remove)
>>>
>>> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
>>> __blkdev_get, which then calls blktrans_open)
>>>
>>> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
>>> calls __register_blkdev)
>>>
>>> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
>>> loop_probe)
>>>
>>> Hence there's an overall dependency of:
>>>
>>> loop_ctl_mutex   ----------> bdev->bd_mutex
>>>         ^                            |
>>>         |                            |
>>>         |                            v
>>> major_names_lock <---------  mtd_table_mutex
>>>
>>> We can break this circular dependency by holding mtd_table_mutex only
>>> for the required critical section in register_mtd_blktrans. This
>>> avoids the mtd_table_mutex -> major_names_lock dependency.
>>>
>>> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
>>> Co-developed-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
>>> ---
>>>
>>> Changes in v1 -> v2:
>>>
>>> Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
>>>
>>>    drivers/mtd/mtd_blkdevs.c | 8 ++------
>>>    1 file changed, 2 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
>>> index fb8e12d590a1..7d26cfe24d05 100644
>>> --- a/drivers/mtd/mtd_blkdevs.c
>>> +++ b/drivers/mtd/mtd_blkdevs.c
>>> @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>>>    	if (!blktrans_notifier.list.next)
>>>    		register_mtd_user(&blktrans_notifier);
>>>    > -
>>> -	mutex_lock(&mtd_table_mutex);
>>> -
>>>    	ret = register_blkdev(tr->major, tr->name);
>>>    	if (ret < 0) {
>>>    		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
>>>    		       tr->name, tr->major, ret);
>>> -		mutex_unlock(&mtd_table_mutex);
>>>    		return ret;
>>>    	}
>>>    > @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>>>    	tr->blkshift = ffs(tr->blksize) - 1;
>>>    >   	INIT_LIST_HEAD(&tr->devs);
>>> -	list_add(&tr->list, &blktrans_majors);
>>>    > +	mutex_lock(&mtd_table_mutex);
>>> +	list_add(&tr->list, &blktrans_majors);
>>>    	mtd_for_each_device(mtd)
>>>    		if (mtd->type != MTD_ABSENT)
>>>    			tr->add_mtd(tr, mtd);
>>> -
>>>    	mutex_unlock(&mtd_table_mutex);
>>>    	return 0;
>>>    }
>>>
>>
>> Hi maintainers,
>>
>> Any chance to review this patch?
>>
>> For additional reference, the mtd_table_mutex --> major_names_lock hierarchy that can be removed by this patch also appears in a different lock chain:
>> https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750
> 
> I'm fine with the patch, but it came too late in the release cycle so
> now I'm waiting -rc1 to apply it.
> 
> Thanks,
> Miquèl
> 

Got it. Thanks for the review, Miquèl.

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Desmond Cheong Zhi Xi]

On 30/6/21 4:43 pm, Miquel Raynal wrote:
> Hello,
> 
> Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> wrote on Wed, 30 Jun
> 2021 16:04:17 +0800:
> 
>> On 18/6/21 12:09 am, Desmond Cheong Zhi Xi wrote:
>>> Syzbot reported a circular locking dependency:
>>> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
>>>
>>> This happens because of the following lock dependencies:
>>>
>>> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
>>> loop_remove, which then calls del_gendisk; this also happens in
>>> loop_exit which eventually calls loop_remove)
>>>
>>> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
>>> __blkdev_get, which then calls blktrans_open)
>>>
>>> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
>>> calls __register_blkdev)
>>>
>>> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
>>> loop_probe)
>>>
>>> Hence there's an overall dependency of:
>>>
>>> loop_ctl_mutex   ----------> bdev->bd_mutex
>>>         ^                            |
>>>         |                            |
>>>         |                            v
>>> major_names_lock <---------  mtd_table_mutex
>>>
>>> We can break this circular dependency by holding mtd_table_mutex only
>>> for the required critical section in register_mtd_blktrans. This
>>> avoids the mtd_table_mutex -> major_names_lock dependency.
>>>
>>> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
>>> Co-developed-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Christoph Hellwig <hch@lst.de>
>>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
>>> ---
>>>
>>> Changes in v1 -> v2:
>>>
>>> Break the circular dependency in register_mtd_blktrans instead of blk_request_module, as suggested by Christoph Hellwig.
>>>
>>>    drivers/mtd/mtd_blkdevs.c | 8 ++------
>>>    1 file changed, 2 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
>>> index fb8e12d590a1..7d26cfe24d05 100644
>>> --- a/drivers/mtd/mtd_blkdevs.c
>>> +++ b/drivers/mtd/mtd_blkdevs.c
>>> @@ -528,14 +528,10 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>>>    	if (!blktrans_notifier.list.next)
>>>    		register_mtd_user(&blktrans_notifier);
>>>    > -
>>> -	mutex_lock(&mtd_table_mutex);
>>> -
>>>    	ret = register_blkdev(tr->major, tr->name);
>>>    	if (ret < 0) {
>>>    		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
>>>    		       tr->name, tr->major, ret);
>>> -		mutex_unlock(&mtd_table_mutex);
>>>    		return ret;
>>>    	}
>>>    > @@ -545,12 +541,12 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
>>>    	tr->blkshift = ffs(tr->blksize) - 1;
>>>    >   	INIT_LIST_HEAD(&tr->devs);
>>> -	list_add(&tr->list, &blktrans_majors);
>>>    > +	mutex_lock(&mtd_table_mutex);
>>> +	list_add(&tr->list, &blktrans_majors);
>>>    	mtd_for_each_device(mtd)
>>>    		if (mtd->type != MTD_ABSENT)
>>>    			tr->add_mtd(tr, mtd);
>>> -
>>>    	mutex_unlock(&mtd_table_mutex);
>>>    	return 0;
>>>    }
>>>
>>
>> Hi maintainers,
>>
>> Any chance to review this patch?
>>
>> For additional reference, the mtd_table_mutex --> major_names_lock hierarchy that can be removed by this patch also appears in a different lock chain:
>> https://syzkaller.appspot.com/bug?id=cbf5fe846f14a90f05e10df200b08c57941dc750
> 
> I'm fine with the patch, but it came too late in the release cycle so
> now I'm waiting -rc1 to apply it.
> 
> Thanks,
> Miquèl
> 

Got it. Thanks for the review, Miquèl.
_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Miquel Raynal]

On Thu, 2021-06-17 at 16:09:04 UTC, Desmond Cheong Zhi Xi wrote:
> Syzbot reported a circular locking dependency:
> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> 
> This happens because of the following lock dependencies:
> 
> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> loop_remove, which then calls del_gendisk; this also happens in
> loop_exit which eventually calls loop_remove)
> 
> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> __blkdev_get, which then calls blktrans_open)
> 
> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> calls __register_blkdev)
> 
> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> loop_probe)
> 
> Hence there's an overall dependency of:
> 
> loop_ctl_mutex   ----------> bdev->bd_mutex
>       ^                            |
>       |                            |
>       |                            v
> major_names_lock <---------  mtd_table_mutex
> 
> We can break this circular dependency by holding mtd_table_mutex only
> for the required critical section in register_mtd_blktrans. This
> avoids the mtd_table_mutex -> major_names_lock dependency.
> 
> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> Co-developed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel

Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Miquel Raynal]

On Thu, 2021-06-17 at 16:09:04 UTC, Desmond Cheong Zhi Xi wrote:
> Syzbot reported a circular locking dependency:
> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> 
> This happens because of the following lock dependencies:
> 
> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> loop_remove, which then calls del_gendisk; this also happens in
> loop_exit which eventually calls loop_remove)
> 
> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> __blkdev_get, which then calls blktrans_open)
> 
> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> calls __register_blkdev)
> 
> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> loop_probe)
> 
> Hence there's an overall dependency of:
> 
> loop_ctl_mutex   ----------> bdev->bd_mutex
>       ^                            |
>       |                            |
>       |                            v
> major_names_lock <---------  mtd_table_mutex
> 
> We can break this circular dependency by holding mtd_table_mutex only
> for the required critical section in register_mtd_blktrans. This
> avoids the mtd_table_mutex -> major_names_lock dependency.
> 
> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> Co-developed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel

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Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans

[Miquel Raynal]

On Thu, 2021-06-17 at 16:09:04 UTC, Desmond Cheong Zhi Xi wrote:
> Syzbot reported a circular locking dependency:
> https://syzkaller.appspot.com/bug?id=7bd106c28e846d1023d4ca915718b1a0905444cb
> 
> This happens because of the following lock dependencies:
> 
> 1. loop_ctl_mutex -> bdev->bd_mutex (when loop_control_ioctl calls
> loop_remove, which then calls del_gendisk; this also happens in
> loop_exit which eventually calls loop_remove)
> 
> 2. bdev->bd_mutex -> mtd_table_mutex (when blkdev_get_by_dev calls
> __blkdev_get, which then calls blktrans_open)
> 
> 3. mtd_table_mutex -> major_names_lock (when register_mtd_blktrans
> calls __register_blkdev)
> 
> 4. major_names_lock -> loop_ctl_mutex (when blk_request_module calls
> loop_probe)
> 
> Hence there's an overall dependency of:
> 
> loop_ctl_mutex   ----------> bdev->bd_mutex
>       ^                            |
>       |                            |
>       |                            v
> major_names_lock <---------  mtd_table_mutex
> 
> We can break this circular dependency by holding mtd_table_mutex only
> for the required critical section in register_mtd_blktrans. This
> avoids the mtd_table_mutex -> major_names_lock dependency.
> 
> Reported-and-tested-by: syzbot+6a8a0d93c91e8fbf2e80@syzkaller.appspotmail.com
> Co-developed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/fixes, thanks.

Miquel
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