Re: [PATCH] badblocks: fix overlapping check for clearing

[NeilBrown]

On Wed, Oct 12 2016, Tomasz Majchrzak wrote:

> On Mon, Oct 10, 2016 at 03:32:58PM -0700, Dan Williams wrote:
>> > On Tue, Sep 06 2016, Tomasz Majchrzak wrote:
>> >> ---
>> >>  block/badblocks.c | 6 --
>> >>  1 file changed, 4 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/block/badblocks.c b/block/badblocks.c
>> >> index 7be53cb..b2ffcc7 100644
>> >> --- a/block/badblocks.c
>> >> +++ b/block/badblocks.c
>> >> @@ -354,7 +354,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, 
>> >> int sectors)
>> >>* current range.  Earlier ranges could also overlap,
>> >>* but only this one can overlap the end of the range.
>> >>*/
>> >> - if (BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) {
>> >> + if ((BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) &&
>> >> + (BB_OFFSET(p[lo]) <= target)) {
>> >
>> > hmmm..
>> > 'target' is the sector just beyond the set of sectors to remove from the
>> > list.
>> > BB_OFFSET(p[lo]) is the first sector in a range that was found in the
>> > list.
>> > If these are equal, then are aren't clearing anything in this range.
>> > So I would have '<', not '<='.
>> >
>> > I don't think this makes the code wrong as we end up assigning to p[lo]
>> > the value that is already there.  But it might be confusing.
>> >
>> >
>> >>   /* Partial overlap, leave the tail of this range */
>> >>   int ack = BB_ACK(p[lo]);
>> >>   sector_t a = BB_OFFSET(p[lo]);
>> >> @@ -377,7 +378,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, 
>> >> int sectors)
>> >>   lo--;
>> >>   }
>> >>   while (lo >= 0 &&
>> >> -BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) {
>> >> +(BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) &&
>> >> +(BB_OFFSET(p[lo]) <= target)) {
>> >
>> > Ditto.
>> >
>> > But the code is, I think, correct. Just not how I would have written it.
>> > So
>> >
>> >  Acked-by: NeilBrown 
>> 
>> I agree with the comments to change "<=" to "<".  Tomasz, care to
>> re-send with those changes?
>
> I have just resent the patch with your suggestions included.
>
>> > In the original md context, it would only ever be called on a block that
>> > was already in the list.
>
> Actually MD RAID10 calls it this way. See handle_write_completed, it iterates
> over all copies and clears the bad block if error has not been returned. I 
> have
> a test case which fails for that reason - existing bad block is modified by
> clear block. It is very unlikely to happen in real life as it depends on
> specific layout of bad blocks and their discovery order, however it's a gap 
> that
> needs to be closed.

Ahh, I didn't realize that.  I see that you are correct though.

>
> I had put some effort to see if clearing of non-existing bad block in RAID10 
> can
> lead to some incorrect behaviour but I haven't found any. It seems that my 
> patch
> is sufficient to fix the problem.

Yes.  Thanks for a lot for sorting this out :-)

NeilBrown


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Re: [PATCH] badblocks: fix overlapping check for clearing

[Tomasz Majchrzak]

On Mon, Oct 10, 2016 at 03:32:58PM -0700, Dan Williams wrote:
> > On Tue, Sep 06 2016, Tomasz Majchrzak wrote:
> >> ---
> >>  block/badblocks.c | 6 --
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/block/badblocks.c b/block/badblocks.c
> >> index 7be53cb..b2ffcc7 100644
> >> --- a/block/badblocks.c
> >> +++ b/block/badblocks.c
> >> @@ -354,7 +354,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, 
> >> int sectors)
> >>* current range.  Earlier ranges could also overlap,
> >>* but only this one can overlap the end of the range.
> >>*/
> >> - if (BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) {
> >> + if ((BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) &&
> >> + (BB_OFFSET(p[lo]) <= target)) {
> >
> > hmmm..
> > 'target' is the sector just beyond the set of sectors to remove from the
> > list.
> > BB_OFFSET(p[lo]) is the first sector in a range that was found in the
> > list.
> > If these are equal, then are aren't clearing anything in this range.
> > So I would have '<', not '<='.
> >
> > I don't think this makes the code wrong as we end up assigning to p[lo]
> > the value that is already there.  But it might be confusing.
> >
> >
> >>   /* Partial overlap, leave the tail of this range */
> >>   int ack = BB_ACK(p[lo]);
> >>   sector_t a = BB_OFFSET(p[lo]);
> >> @@ -377,7 +378,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, 
> >> int sectors)
> >>   lo--;
> >>   }
> >>   while (lo >= 0 &&
> >> -BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) {
> >> +(BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) &&
> >> +(BB_OFFSET(p[lo]) <= target)) {
> >
> > Ditto.
> >
> > But the code is, I think, correct. Just not how I would have written it.
> > So
> >
> >  Acked-by: NeilBrown 
> 
> I agree with the comments to change "<=" to "<".  Tomasz, care to
> re-send with those changes?

I have just resent the patch with your suggestions included.

> > In the original md context, it would only ever be called on a block that
> > was already in the list.

Actually MD RAID10 calls it this way. See handle_write_completed, it iterates
over all copies and clears the bad block if error has not been returned. I have
a test case which fails for that reason - existing bad block is modified by
clear block. It is very unlikely to happen in real life as it depends on
specific layout of bad blocks and their discovery order, however it's a gap that
needs to be closed.

I had put some effort to see if clearing of non-existing bad block in RAID10 can
lead to some incorrect behaviour but I haven't found any. It seems that my patch
is sufficient to fix the problem.

Tomek
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Re: [PATCH] badblocks: fix overlapping check for clearing

[NeilBrown]

On Tue, Sep 06 2016, Tomasz Majchrzak wrote:

> Current bad block clear implementation assumes the range to clear
> overlaps with at least one bad block already stored. If given range to
> clear precedes first bad block in a list, the first entry is incorrectly
> updated.

In the original md context, it would only ever be called on a block that
was already in the list.
But you are right that it is best not to assume this, and to code more
safely.



>
> Check not only if stored block end is past clear block end but also if
> stored block start is before clear block end.
>
> Signed-off-by: Tomasz Majchrzak 

Dan Williams seems to have taken responsibility for this code through
his nvdimm tree, so I've added him to 'cc' in the hope that he looks at
this (I wonder if he is even on linux-block )


> ---
>  block/badblocks.c | 6 --
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/block/badblocks.c b/block/badblocks.c
> index 7be53cb..b2ffcc7 100644
> --- a/block/badblocks.c
> +++ b/block/badblocks.c
> @@ -354,7 +354,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, int 
> sectors)
>* current range.  Earlier ranges could also overlap,
>* but only this one can overlap the end of the range.
>*/
> - if (BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) {
> + if ((BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) &&
> + (BB_OFFSET(p[lo]) <= target)) {

hmmm..
'target' is the sector just beyond the set of sectors to remove from the
list.
BB_OFFSET(p[lo]) is the first sector in a range that was found in the
list.
If these are equal, then are aren't clearing anything in this range.
So I would have '<', not '<='.

I don't think this makes the code wrong as we end up assigning to p[lo]
the value that is already there.  But it might be confusing.


>   /* Partial overlap, leave the tail of this range */
>   int ack = BB_ACK(p[lo]);
>   sector_t a = BB_OFFSET(p[lo]);
> @@ -377,7 +378,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, int 
> sectors)
>   lo--;
>   }
>   while (lo >= 0 &&
> -BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) {
> +(BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) &&
> +(BB_OFFSET(p[lo]) <= target)) {

Ditto.

But the code is, I think, correct. Just not how I would have written it.
So

 Acked-by: NeilBrown 

Thanks,
NeilBrown


>   /* This range does overlap */
>   if (BB_OFFSET(p[lo]) < s) {
>   /* Keep the early parts of this range. */
> -- 
> 1.8.3.1


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[PATCH] badblocks: fix overlapping check for clearing

[Tomasz Majchrzak]

Current bad block clear implementation assumes the range to clear
overlaps with at least one bad block already stored. If given range to
clear precedes first bad block in a list, the first entry is incorrectly
updated.

Check not only if stored block end is past clear block end but also if
stored block start is before clear block end.

Signed-off-by: Tomasz Majchrzak 
---
 block/badblocks.c | 6 --
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/badblocks.c b/block/badblocks.c
index 7be53cb..b2ffcc7 100644
--- a/block/badblocks.c
+++ b/block/badblocks.c
@@ -354,7 +354,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, int 
sectors)
 * current range.  Earlier ranges could also overlap,
 * but only this one can overlap the end of the range.
 */
-   if (BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) {
+   if ((BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > target) &&
+   (BB_OFFSET(p[lo]) <= target)) {
/* Partial overlap, leave the tail of this range */
int ack = BB_ACK(p[lo]);
sector_t a = BB_OFFSET(p[lo]);
@@ -377,7 +378,8 @@ int badblocks_clear(struct badblocks *bb, sector_t s, int 
sectors)
lo--;
}
while (lo >= 0 &&
-  BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) {
+  (BB_OFFSET(p[lo]) + BB_LEN(p[lo]) > s) &&
+  (BB_OFFSET(p[lo]) <= target)) {
/* This range does overlap */
if (BB_OFFSET(p[lo]) < s) {
/* Keep the early parts of this range. */
-- 
1.8.3.1

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