[PATCH] md/raid5: recheck if reshape has finished with device_lock held

[PATCH] md/raid5: recheck if reshape has finished with device_lock held

[Benjamin Marzinski]

When handling an IO request, MD checks if a reshape is currently
happening, and if so, where the IO sector is in relation to the reshape
progress. MD uses conf->reshape_progress for both of these tasks.  When
the reshape finishes, conf->reshape_progress is set to MaxSector.  If
this occurs after MD checks if the reshape is currently happening but
before it calls ahead_of_reshape(), then ahead_of_reshape() will end up
comparing the IO sector against MaxSector. During a backwards reshape,
this will make MD think the IO sector is in the area not yet reshaped,
causing it to use the previous configuration, and map the IO to the
sector where that data was before the reshape.

This bug can be triggered by running the lvm2
lvconvert-raid-reshape-linear_to_raid6-single-type.sh test in a loop,
although it's very hard to reproduce.

Fix this by rechecking if the reshape has finished after grabbing the
device_lock.

Fixes: fef9c61fdfabf ("md/raid5: change reshape-progress measurement to cope with reshaping backwards.")
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
---
 drivers/md/raid5.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 547fd15115cd..65d9b1ca815c 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5923,15 +5923,17 @@ static enum stripe_result make_stripe_request(struct mddev *mddev,
 		 * to check again.
 		 */
 		spin_lock_irq(&conf->device_lock);
-		if (ahead_of_reshape(mddev, logical_sector,
-				     conf->reshape_progress)) {
-			previous = 1;
-		} else {
+		if (conf->reshape_progress != MaxSector) {
 			if (ahead_of_reshape(mddev, logical_sector,
-					     conf->reshape_safe)) {
-				spin_unlock_irq(&conf->device_lock);
-				ret = STRIPE_SCHEDULE_AND_RETRY;
-				goto out;
+					     conf->reshape_progress)) {
+				previous = 1;
+			} else {
+				if (ahead_of_reshape(mddev, logical_sector,
+						     conf->reshape_safe)) {
+					spin_unlock_irq(&conf->device_lock);
+					ret = STRIPE_SCHEDULE_AND_RETRY;
+					goto out;
+				}
 			}
 		}
 		spin_unlock_irq(&conf->device_lock);
-- 
2.43.5

Re: [PATCH] md/raid5: recheck if reshape has finished with device_lock held

[Yu Kuai]

Hi,

在 2024/06/27 13:37, Benjamin Marzinski 写道:
> When handling an IO request, MD checks if a reshape is currently
> happening, and if so, where the IO sector is in relation to the reshape
> progress. MD uses conf->reshape_progress for both of these tasks.  When
> the reshape finishes, conf->reshape_progress is set to MaxSector.  If
> this occurs after MD checks if the reshape is currently happening but
> before it calls ahead_of_reshape(), then ahead_of_reshape() will end up
> comparing the IO sector against MaxSector. During a backwards reshape,
> this will make MD think the IO sector is in the area not yet reshaped,
> causing it to use the previous configuration, and map the IO to the
> sector where that data was before the reshape.
> 
> This bug can be triggered by running the lvm2
> lvconvert-raid-reshape-linear_to_raid6-single-type.sh test in a loop,
> although it's very hard to reproduce.
> 
> Fix this by rechecking if the reshape has finished after grabbing the
> device_lock.
> 
> Fixes: fef9c61fdfabf ("md/raid5: change reshape-progress measurement to cope with reshaping backwards.")
> Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
> ---
>   drivers/md/raid5.c | 18 ++++++++++--------
>   1 file changed, 10 insertions(+), 8 deletions(-)
> 

Thanks for the patch, it looks correct. However, can you factor out a
helper and make the code more readable? The code is already quite
complicated.

Thanks,
Kuai

> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 547fd15115cd..65d9b1ca815c 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5923,15 +5923,17 @@ static enum stripe_result make_stripe_request(struct mddev *mddev,
>   		 * to check again.
>   		 */
>   		spin_lock_irq(&conf->device_lock);
> -		if (ahead_of_reshape(mddev, logical_sector,
> -				     conf->reshape_progress)) {
> -			previous = 1;
> -		} else {
> +		if (conf->reshape_progress != MaxSector) {
>   			if (ahead_of_reshape(mddev, logical_sector,
> -					     conf->reshape_safe)) {
> -				spin_unlock_irq(&conf->device_lock);
> -				ret = STRIPE_SCHEDULE_AND_RETRY;
> -				goto out;
> +					     conf->reshape_progress)) {
> +				previous = 1;
> +			} else {
> +				if (ahead_of_reshape(mddev, logical_sector,
> +						     conf->reshape_safe)) {
> +					spin_unlock_irq(&conf->device_lock);
> +					ret = STRIPE_SCHEDULE_AND_RETRY;
> +					goto out;
> +				}
>   			}
>   		}
>   		spin_unlock_irq(&conf->device_lock);
> 

Re: [PATCH] md/raid5: recheck if reshape has finished with device_lock held

[Benjamin Marzinski]

On Thu, Jun 27, 2024 at 08:17:51PM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2024/06/27 13:37, Benjamin Marzinski 写道:
> > When handling an IO request, MD checks if a reshape is currently
> > happening, and if so, where the IO sector is in relation to the reshape
> > progress. MD uses conf->reshape_progress for both of these tasks.  When
> > the reshape finishes, conf->reshape_progress is set to MaxSector.  If
> > this occurs after MD checks if the reshape is currently happening but
> > before it calls ahead_of_reshape(), then ahead_of_reshape() will end up
> > comparing the IO sector against MaxSector. During a backwards reshape,
> > this will make MD think the IO sector is in the area not yet reshaped,
> > causing it to use the previous configuration, and map the IO to the
> > sector where that data was before the reshape.
> > 
> > This bug can be triggered by running the lvm2
> > lvconvert-raid-reshape-linear_to_raid6-single-type.sh test in a loop,
> > although it's very hard to reproduce.
> > 
> > Fix this by rechecking if the reshape has finished after grabbing the
> > device_lock.
> > 
> > Fixes: fef9c61fdfabf ("md/raid5: change reshape-progress measurement to cope with reshaping backwards.")
> > Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
> > ---
> >   drivers/md/raid5.c | 18 ++++++++++--------
> >   1 file changed, 10 insertions(+), 8 deletions(-)
> > 
> 
> Thanks for the patch, it looks correct. However, can you factor out a
> helper and make the code more readable? The code is already quite
> complicated.

Sure.
 
> Thanks,
> Kuai
> 
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index 547fd15115cd..65d9b1ca815c 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -5923,15 +5923,17 @@ static enum stripe_result make_stripe_request(struct mddev *mddev,
> >   		 * to check again.
> >   		 */
> >   		spin_lock_irq(&conf->device_lock);
> > -		if (ahead_of_reshape(mddev, logical_sector,
> > -				     conf->reshape_progress)) {
> > -			previous = 1;
> > -		} else {
> > +		if (conf->reshape_progress != MaxSector) {
> >   			if (ahead_of_reshape(mddev, logical_sector,
> > -					     conf->reshape_safe)) {
> > -				spin_unlock_irq(&conf->device_lock);
> > -				ret = STRIPE_SCHEDULE_AND_RETRY;
> > -				goto out;
> > +					     conf->reshape_progress)) {
> > +				previous = 1;
> > +			} else {
> > +				if (ahead_of_reshape(mddev, logical_sector,
> > +						     conf->reshape_safe)) {
> > +					spin_unlock_irq(&conf->device_lock);
> > +					ret = STRIPE_SCHEDULE_AND_RETRY;
> > +					goto out;
> > +				}
> >   			}
> >   		}
> >   		spin_unlock_irq(&conf->device_lock);
> >