linux-kernel - Re: [PATCH 5.10] btrfs: fix region size in count_bitmap

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Date:   Tue, 3 Oct 2023 15:48:11 +0300
From:   Анастасия Любимова 
        <abelova@...ralinux.ru>
To:     Chris Mason <clm@...com>
Cc:     Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Dennis Zhou <dennis@...nel.org>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 5.10] btrfs: fix region size in count_bitmap_extents


03/10/23 15:39, Anastasia Belova пишет:
>
> 14/09/23 12:45, Anastasia Belova пишет:
>> count_bitmap_extents was deleted in version 5.11, but
>> there is possible mistake in versions 5.6-5.10.
>>
>> Region size should be calculated by subtracting
>> the end from the beginning.
> Do I understand correctly that bytes should decrease and
> (rs - re) is always negative and should be replaced by (re - rs)?
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Fixes: dfb79ddb130e ("btrfs: track discardable extents for async discard")
>> Signed-off-by: Anastasia Belova<abelova@...ralinux.ru>
>> ---
>>   fs/btrfs/free-space-cache.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
>> index 4989c60b1df9..a34e266a0969 100644
>> --- a/fs/btrfs/free-space-cache.c
>> +++ b/fs/btrfs/free-space-cache.c
>> @@ -1930,7 +1930,7 @@ static int count_bitmap_extents(struct btrfs_free_space_ctl *ctl,
>>   
>>   	bitmap_for_each_set_region(bitmap_info->bitmap, rs, re, 0,
>>   				   BITS_PER_BITMAP) {
>> -		bytes -= (rs - re) * ctl->unit;
>> +		bytes -= (re - rs) * ctl->unit;
>>   		count++;
>>   
>>   		if (!bytes)
> Anastasia
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