Re: [PATCH] btrfs: volumes: Increase bioc pointer check

[Qu Wenruo]

On 2022/10/25 17:29, Nikolay Borisov wrote:
> On 25.10.22 г. 11:28 ч., Li zeming wrote:
> > If kzalloc fails to allocate the bioc pointer, NULL is returned
> > directly.
> >
> > Signed-off-by: Li zeming <zeming@xxxxxxxxxxxx>
>
> 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
> > ---
> >   fs/btrfs/volumes.c | 2 ++
> >   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_
> >            */
> >           sizeof(u64) * (total_stripes),
> >           GFP_NOFS|__GFP_NOFAIL);
> > +    if (!bioc)
> > +        return NULL;
> >       atomic_set(&bioc->error, 0);
> >       refcount_set(&bioc->refs, 1);