Re: [PATCH RESEND] bpf: fix order of args in call to bpf_map_kvcalloc

[Suren Baghdasaryan]

On Tue, Jul 9, 2024 at 8:14 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> On 7/8/24 10:20 AM, Linux regression tracking (Thorsten Leemhuis) wrote:
> > [CCing the regressions list and people mentioned below]
> >
> > On 12.06.24 16:53, Alexei Starovoitov wrote:
> >> On Wed, Jun 12, 2024 at 2:51 AM Mohammad Shehar Yaar Tausif
> >> <sheharyaar48@xxxxxxxxx> wrote:
> >>>
> >>> The original function call passed size of smap->bucket before the number of
> >>> buckets which raises the error 'calloc-transposed-args' on compilation.
> >>>
> >>> Fixes: 62827d612ae5 ("bpf: Remove __bpf_local_storage_map_alloc")
> >>> Reviewed-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> >>> Signed-off-by: Mohammad Shehar Yaar Tausif <sheharyaar48@xxxxxxxxx>
> >>> ---
> >>> - already merged in linux-next
> >>> - [1] suggested sending as a fix for 6.10 cycle
> >>
> >> No. It's not a fix.
> >
> > If you have a minute, could you please explain why that is? From what I
> > can see a quite a few people run into build problems with 6.10-rc
> > recently that are fixed by the patch:
> >
> > * Péter Ujfalusi
> > https://lore.kernel.org/bpf/363ad8d1-a2d2-4fca-b66a-3d838eb5def9@xxxxxxxxx/
> >
> > * Christian Kujau
> > https://lore.kernel.org/bpf/48360912-b239-51f2-8f25-07a46516dc76@xxxxxxxxxxxxxxx/
> > https://lore.kernel.org/lkml/d0dd2457-ab58-1b08-caa4-93eaa2de221e@xxxxxxxxxxxxxxx/
> >
> > * Lorenzo Stoakes
> > https://fosstodon.org/@ljs@xxxxxxxxxxxxxxxxx/112734050799590482
> >
> > At the same time I see that the culprit mentioned above is from 6.4-rc1,
>
> IIUC the order was wrong even before, but see below.
>
> > so I guess it there must be some other reason why a few people seem to
> > tun into this now. Did some other change expose this problem? Or are
> > updated compilers causing this?
>
> I think it's because of 2c321f3f70bc ("mm: change inlined allocation helpers
> to account at the call site"), which was added in 6.10-rc1 and thus makes
> this technically a 6.10 regression after all.

IIUC the above mentioned change reveals a problem that was there
before the change. So, it's a build regression in 6.10 because the bug
got exposed but the bug was introduced much earlier. The fix should be
marked as:

Fixes: ddef81b5fd1d ("bpf: use bpf_map_kvcalloc in bpf_local_storage")

> So what triggers the bug is
> AFAICS the following together:
>
> - gcc-14 (didn't see it with gcc-13)
> - commit 2c321f3f70bc that makes bpf_map_kvcalloc a macro that does
> kvcalloc() directly instead of static inline function wrapping it for
> !CONFIG_MEMCG
> - CONFIG_MEMCG=n in .config
>
> The fix is so trivial, it's better to include it in 6.10 even this late.
>
> > Ciao, Thorsten
> >
> >>> [1] https://lore.kernel.org/all/363ad8d1-a2d2-4fca-b66a-3d838eb5def9@xxxxxxxxx/
> >>> ---
> >>>  kernel/bpf/bpf_local_storage.c | 4 ++--
> >>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> >>> index 976cb258a0ed..c938dea5ddbf 100644
> >>> --- a/kernel/bpf/bpf_local_storage.c
> >>> +++ b/kernel/bpf/bpf_local_storage.c
> >>> @@ -782,8 +782,8 @@ bpf_local_storage_map_alloc(union bpf_attr *attr,
> >>>         nbuckets = max_t(u32, 2, nbuckets);
> >>>         smap->bucket_log = ilog2(nbuckets);
> >>>
> >>> -       smap->buckets = bpf_map_kvcalloc(&smap->map, sizeof(*smap->buckets),
> >>> -                                        nbuckets, GFP_USER | __GFP_NOWARN);
> >>> +       smap->buckets = bpf_map_kvcalloc(&smap->map, nbuckets,
> >>> +                                        sizeof(*smap->buckets), GFP_USER | __GFP_NOWARN);
> >>>         if (!smap->buckets) {
> >>>                 err = -ENOMEM;
> >>>                 goto free_smap;
> >>>
> >>> ---
> >>> base-commit: 2ef5971ff345d3c000873725db555085e0131961
> >>> change-id: 20240612-master-fe9e63ab5c95
> >>>
> >>> Best regards,
> >>> --
> >>> Mohammad Shehar Yaar Tausif <sheharyaar48@xxxxxxxxx>
> >>>
>