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Message-ID: <13035b03-ed27-c36e-da6a-072d882e787f@gmx.com>
Date:   Tue, 25 Oct 2022 17:49:55 +0800
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Subject: Re: [PATCH] btrfs: volumes: Increase bioc pointer check
Content-Language: en-US
To:     Nikolay Borisov <nborisov@suse.com>,
        Li zeming <zeming@nfschina.com>, clm@fb.com,
        josef@toxicpanda.com, dsterba@suse.com
Cc:     linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20221025082835.3751-1-zeming@nfschina.com>
 <1d9d4d78-073d-fc49-1918-f7c8ab6fe15e@suse.com>
From:   Qu Wenruo <quwenruo.btrfs@gmx.com>
In-Reply-To: <1d9d4d78-073d-fc49-1918-f7c8ab6fe15e@suse.com>
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On 2022/10/25 17:29, Nikolay Borisov wrote:
>
>
> On 25.10.22 =D0=B3. 11:28 =D1=87., Li zeming wrote:
>> If kzalloc fails to allocate the bioc pointer, NULL is returned
>> directly.
>>
>> Signed-off-by: Li zeming <zeming@nfschina.com>
>
> This patch clearly shows you haven't really understood the code. As is
> evident there is __GFP_NOFAIL flag so as per the guarantees for this
> flag we either loop infinitely trying to allocate a bioc or simply
> allocated it. So this check can never be triggered.

I guess what he missed is just to also remove that NOFAIL flag.

NOFAIL will not 100% guarantee the allocation, and I don't see this
location to be so important, especially when the only caller is already
handing allocation failure.

Thanks,
Qu

>
> NAK
>> ---
>> =C2=A0 fs/btrfs/volumes.c | 2 ++
>> =C2=A0 1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 064ab2a79c80..f9cb815fe23d 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -5892,6 +5892,8 @@ static struct btrfs_io_context
>> *alloc_btrfs_io_context(struct btrfs_fs_info *fs_
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 sizeof(u64) * (t=
otal_stripes),
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 GFP_NOFS|__GFP_N=
OFAIL);
>> +=C2=A0=C2=A0=C2=A0 if (!bioc)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return NULL;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 atomic_set(&bioc->error, 0);
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 refcount_set(&bioc->refs, 1);