[PATCH] btrfs: zoned: fix bitops api misuse

[PATCH] btrfs: zoned: fix bitops api misuse

[Naohiro Aota]

From: Naohiro Aota <naohiro.aota@wdc.com>

find_next_bit and find_next_zero_bit take @size as the second parameter and
@offset as the third parameter. They are specified opposite in
btrfs_ensure_empty_zones(). Thanks to the later loop, it never failed to
detect the empty zones. Fix them and (maybe) return the result a bit
faster.

Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
CC: stable@vger.kernel.org # 5.15+
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
 fs/btrfs/zoned.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index 2b160fda7301..55bde1336d81 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -1171,12 +1171,12 @@ int btrfs_ensure_empty_zones(struct btrfs_device *device, u64 start, u64 size)
 		return -ERANGE;
 
 	/* All the zones are conventional */
-	if (find_next_bit(zinfo->seq_zones, begin, end) == end)
+	if (find_next_bit(zinfo->seq_zones, end, begin) == end)
 		return 0;
 
 	/* All the zones are sequential and empty */
-	if (find_next_zero_bit(zinfo->seq_zones, begin, end) == end &&
-	    find_next_zero_bit(zinfo->empty_zones, begin, end) == end)
+	if (find_next_zero_bit(zinfo->seq_zones, end, begin) == end &&
+	    find_next_zero_bit(zinfo->empty_zones, end, begin) == end)
 		return 0;
 
 	for (pos = start; pos < start + size; pos += zinfo->zone_size) {
-- 
2.40.0

Re: [PATCH] btrfs: zoned: fix bitops api misuse

[David Sterba]

On Tue, Apr 18, 2023 at 05:45:24PM +0900, Naohiro Aota wrote:
> From: Naohiro Aota <naohiro.aota@wdc.com>
> 
> find_next_bit and find_next_zero_bit take @size as the second parameter and
> @offset as the third parameter. They are specified opposite in
> btrfs_ensure_empty_zones(). Thanks to the later loop, it never failed to
> detect the empty zones. Fix them and (maybe) return the result a bit
> faster.
> 
> Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
> CC: stable@vger.kernel.org # 5.15+
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> ---
>  fs/btrfs/zoned.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 2b160fda7301..55bde1336d81 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -1171,12 +1171,12 @@ int btrfs_ensure_empty_zones(struct btrfs_device *device, u64 start, u64 size)
>  		return -ERANGE;
>  
>  	/* All the zones are conventional */
> -	if (find_next_bit(zinfo->seq_zones, begin, end) == end)
> +	if (find_next_bit(zinfo->seq_zones, end, begin) == end)

End is defined as "end = (start + size) >> shift", and the 2nd parameter
of find_next_bit is supposed to be 'size'. Shouldn't it be "size >>
shift"?

Re: [PATCH] btrfs: zoned: fix bitops api misuse

[Naohiro Aota]

On Wed, Apr 19, 2023 at 01:24:56AM +0200, David Sterba wrote:
> On Tue, Apr 18, 2023 at 05:45:24PM +0900, Naohiro Aota wrote:
> > From: Naohiro Aota <naohiro.aota@wdc.com>
> > 
> > find_next_bit and find_next_zero_bit take @size as the second parameter and
> > @offset as the third parameter. They are specified opposite in
> > btrfs_ensure_empty_zones(). Thanks to the later loop, it never failed to
> > detect the empty zones. Fix them and (maybe) return the result a bit
> > faster.
> > 
> > Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
> > CC: stable@vger.kernel.org # 5.15+
> > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> > ---
> >  fs/btrfs/zoned.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> > index 2b160fda7301..55bde1336d81 100644
> > --- a/fs/btrfs/zoned.c
> > +++ b/fs/btrfs/zoned.c
> > @@ -1171,12 +1171,12 @@ int btrfs_ensure_empty_zones(struct btrfs_device *device, u64 start, u64 size)
> >  		return -ERANGE;
> >  
> >  	/* All the zones are conventional */
> > -	if (find_next_bit(zinfo->seq_zones, begin, end) == end)
> > +	if (find_next_bit(zinfo->seq_zones, end, begin) == end)
> 
> End is defined as "end = (start + size) >> shift", and the 2nd parameter
> of find_next_bit is supposed to be 'size'. Shouldn't it be "size >>
> shift"?

Not so. The argument "size" represents the size of the allocation range,
which is to be confirmed as empty. OTOH, find_next_bit()'s "size" (the 2nd
parameter) represents the size of an entire bitmap, not the number of bits to
be tested.

Re: [PATCH] btrfs: zoned: fix bitops api misuse

[Naohiro Aota]

On Thu, Apr 20, 2023 at 12:58:14PM +0900, Naohiro Aota wrote:
> On Wed, Apr 19, 2023 at 01:24:56AM +0200, David Sterba wrote:
> > On Tue, Apr 18, 2023 at 05:45:24PM +0900, Naohiro Aota wrote:
> > > From: Naohiro Aota <naohiro.aota@wdc.com>
> > > 
> > > find_next_bit and find_next_zero_bit take @size as the second parameter and
> > > @offset as the third parameter. They are specified opposite in
> > > btrfs_ensure_empty_zones(). Thanks to the later loop, it never failed to
> > > detect the empty zones. Fix them and (maybe) return the result a bit
> > > faster.
> > > 
> > > Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
> > > CC: stable@vger.kernel.org # 5.15+
> > > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> > > ---
> > >  fs/btrfs/zoned.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> > > index 2b160fda7301..55bde1336d81 100644
> > > --- a/fs/btrfs/zoned.c
> > > +++ b/fs/btrfs/zoned.c
> > > @@ -1171,12 +1171,12 @@ int btrfs_ensure_empty_zones(struct btrfs_device *device, u64 start, u64 size)
> > >  		return -ERANGE;
> > >  
> > >  	/* All the zones are conventional */
> > > -	if (find_next_bit(zinfo->seq_zones, begin, end) == end)
> > > +	if (find_next_bit(zinfo->seq_zones, end, begin) == end)
> > 
> > End is defined as "end = (start + size) >> shift", and the 2nd parameter
> > of find_next_bit is supposed to be 'size'. Shouldn't it be "size >>
> > shift"?
> 
> Not so. The argument "size" represents the size of the allocation range,
> which is to be confirmed as empty. OTOH, find_next_bit()'s "size" (the 2nd
> parameter) represents the size of an entire bitmap, not the number of bits to
> be tested.

BTW, I found the same logic is implemented in subpage.c as
bitmap_test_range_all_{set,zero}. So, it might worth moving them to
somewhere (misc.h?) and use them here.

Re: [PATCH] btrfs: zoned: fix bitops api misuse

[David Sterba]

On Thu, Apr 20, 2023 at 01:14:30PM +0900, Naohiro Aota wrote:
> On Thu, Apr 20, 2023 at 12:58:14PM +0900, Naohiro Aota wrote:
> > On Wed, Apr 19, 2023 at 01:24:56AM +0200, David Sterba wrote:
> > > On Tue, Apr 18, 2023 at 05:45:24PM +0900, Naohiro Aota wrote:
> > > > From: Naohiro Aota <naohiro.aota@wdc.com>
> > > > 
> > > > find_next_bit and find_next_zero_bit take @size as the second parameter and
> > > > @offset as the third parameter. They are specified opposite in
> > > > btrfs_ensure_empty_zones(). Thanks to the later loop, it never failed to
> > > > detect the empty zones. Fix them and (maybe) return the result a bit
> > > > faster.
> > > > 
> > > > Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
> > > > CC: stable@vger.kernel.org # 5.15+
> > > > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> > > > ---
> > > >  fs/btrfs/zoned.c | 6 +++---
> > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> > > > index 2b160fda7301..55bde1336d81 100644
> > > > --- a/fs/btrfs/zoned.c
> > > > +++ b/fs/btrfs/zoned.c
> > > > @@ -1171,12 +1171,12 @@ int btrfs_ensure_empty_zones(struct btrfs_device *device, u64 start, u64 size)
> > > >  		return -ERANGE;
> > > >  
> > > >  	/* All the zones are conventional */
> > > > -	if (find_next_bit(zinfo->seq_zones, begin, end) == end)
> > > > +	if (find_next_bit(zinfo->seq_zones, end, begin) == end)
> > > 
> > > End is defined as "end = (start + size) >> shift", and the 2nd parameter
> > > of find_next_bit is supposed to be 'size'. Shouldn't it be "size >>
> > > shift"?
> > 
> > Not so. The argument "size" represents the size of the allocation range,
> > which is to be confirmed as empty. OTOH, find_next_bit()'s "size" (the 2nd
> > parameter) represents the size of an entire bitmap, not the number of bits to
> > be tested.
> 
> BTW, I found the same logic is implemented in subpage.c as
> bitmap_test_range_all_{set,zero}. So, it might worth moving them to
> somewhere (misc.h?) and use them here.

Good idea, please send it as a separate patch. Thanks.