* [PATCH v2] mtd: break circular locks in register_mtd_blktrans
@ 2021-06-17 16:09 ` Desmond Cheong Zhi Xi
0 siblings, 0 replies; 15+ messages in thread
From: Desmond Cheong Zhi Xi @ 2021-06-17 16:09 UTC (permalink / raw)
To: miquel.raynal, richard, vigneshr
Cc: linux-kernel, syzbot+6a8a0d93c91e8fbf2e80, linux-mtd,
Desmond Cheong Zhi Xi, linux-kernel-mentees, Christoph Hellwig
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
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^ permalink raw reply related [flat|nested] 15+ messages in thread* [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-17 16:09 ` Desmond Cheong Zhi Xi 0 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-17 16:09 UTC (permalink / raw) To: miquel.raynal, richard, vigneshr Cc: Desmond Cheong Zhi Xi, linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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 ^ permalink raw reply related [flat|nested] 15+ messages in thread
* [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-17 16:09 ` Desmond Cheong Zhi Xi 0 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-17 16:09 UTC (permalink / raw) To: miquel.raynal, richard, vigneshr Cc: Desmond Cheong Zhi Xi, linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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/ ^ permalink raw reply related [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans 2021-06-17 16:09 ` Desmond Cheong Zhi Xi (?) @ 2021-06-30 8:04 ` Desmond Cheong Zhi Xi -1 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-30 8:04 UTC (permalink / raw) To: miquel.raynal, richard, vigneshr Cc: linux-kernel, syzbot+6a8a0d93c91e8fbf2e80, linux-mtd, linux-kernel-mentees, Christoph Hellwig 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 ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-30 8:04 ` Desmond Cheong Zhi Xi 0 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-30 8:04 UTC (permalink / raw) To: miquel.raynal, richard, vigneshr Cc: linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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 ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-30 8:04 ` Desmond Cheong Zhi Xi 0 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-30 8:04 UTC (permalink / raw) To: miquel.raynal, richard, vigneshr Cc: linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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/ ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans 2021-06-30 8:04 ` Desmond Cheong Zhi Xi (?) @ 2021-06-30 8:43 ` Miquel Raynal -1 siblings, 0 replies; 15+ messages in thread From: Miquel Raynal @ 2021-06-30 8:43 UTC (permalink / raw) To: Desmond Cheong Zhi Xi Cc: vigneshr, richard, linux-kernel, syzbot+6a8a0d93c91e8fbf2e80, linux-mtd, linux-kernel-mentees, Christoph Hellwig 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 ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-30 8:43 ` Miquel Raynal 0 siblings, 0 replies; 15+ messages in thread From: Miquel Raynal @ 2021-06-30 8:43 UTC (permalink / raw) To: Desmond Cheong Zhi Xi Cc: richard, vigneshr, linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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 ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-30 8:43 ` Miquel Raynal 0 siblings, 0 replies; 15+ messages in thread From: Miquel Raynal @ 2021-06-30 8:43 UTC (permalink / raw) To: Desmond Cheong Zhi Xi Cc: richard, vigneshr, linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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/ ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans 2021-06-30 8:43 ` Miquel Raynal (?) @ 2021-06-30 9:21 ` Desmond Cheong Zhi Xi -1 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-30 9:21 UTC (permalink / raw) To: Miquel Raynal Cc: vigneshr, richard, linux-kernel, syzbot+6a8a0d93c91e8fbf2e80, linux-mtd, linux-kernel-mentees, Christoph Hellwig 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 ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-30 9:21 ` Desmond Cheong Zhi Xi 0 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-30 9:21 UTC (permalink / raw) To: Miquel Raynal Cc: richard, vigneshr, linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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. ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-06-30 9:21 ` Desmond Cheong Zhi Xi 0 siblings, 0 replies; 15+ messages in thread From: Desmond Cheong Zhi Xi @ 2021-06-30 9:21 UTC (permalink / raw) To: Miquel Raynal Cc: richard, vigneshr, linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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/ ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans 2021-06-17 16:09 ` Desmond Cheong Zhi Xi (?) @ 2021-07-15 22:50 ` Miquel Raynal -1 siblings, 0 replies; 15+ messages in thread From: Miquel Raynal @ 2021-07-15 22:50 UTC (permalink / raw) To: Desmond Cheong Zhi Xi, miquel.raynal, richard, vigneshr Cc: linux-kernel, syzbot+6a8a0d93c91e8fbf2e80, linux-mtd, linux-kernel-mentees, Christoph Hellwig 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 _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-07-15 22:50 ` Miquel Raynal 0 siblings, 0 replies; 15+ messages in thread From: Miquel Raynal @ 2021-07-15 22:50 UTC (permalink / raw) To: Desmond Cheong Zhi Xi, miquel.raynal, richard, vigneshr Cc: linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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 ^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH v2] mtd: break circular locks in register_mtd_blktrans @ 2021-07-15 22:50 ` Miquel Raynal 0 siblings, 0 replies; 15+ messages in thread From: Miquel Raynal @ 2021-07-15 22:50 UTC (permalink / raw) To: Desmond Cheong Zhi Xi, miquel.raynal, richard, vigneshr Cc: linux-mtd, linux-kernel, skhan, gregkh, linux-kernel-mentees, syzbot+6a8a0d93c91e8fbf2e80, Christoph Hellwig 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 ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/ ^ permalink raw reply [flat|nested] 15+ messages in thread
end of thread, other threads:[~2021-07-15 22:53 UTC | newest] Thread overview: 15+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2021-06-17 16:09 [PATCH v2] mtd: break circular locks in register_mtd_blktrans Desmond Cheong Zhi Xi 2021-06-17 16:09 ` Desmond Cheong Zhi Xi 2021-06-17 16:09 ` Desmond Cheong Zhi Xi 2021-06-30 8:04 ` Desmond Cheong Zhi Xi 2021-06-30 8:04 ` Desmond Cheong Zhi Xi 2021-06-30 8:04 ` Desmond Cheong Zhi Xi 2021-06-30 8:43 ` Miquel Raynal 2021-06-30 8:43 ` Miquel Raynal 2021-06-30 8:43 ` Miquel Raynal 2021-06-30 9:21 ` Desmond Cheong Zhi Xi 2021-06-30 9:21 ` Desmond Cheong Zhi Xi 2021-06-30 9:21 ` Desmond Cheong Zhi Xi 2021-07-15 22:50 ` Miquel Raynal 2021-07-15 22:50 ` Miquel Raynal 2021-07-15 22:50 ` Miquel Raynal
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