Re: [Xen-devel] [PATCH v2 19/21] treewide: add checks for the return value of memblock_alloc*()

[Christophe Leroy <christophe.leroy@xxxxxx>]

Le 31/01/2019 à 07:41, Mike Rapoport a écrit :
> On Thu, Jan 31, 2019 at 07:07:46AM +0100, Christophe Leroy wrote:
> > Le 21/01/2019 à 09:04, Mike Rapoport a écrit :
> > > Add check for the return value of memblock_alloc*() functions and call
> > > panic() in case of error.
> > > The panic message repeats the one used by panicing memblock allocators with
> > > adjustment of parameters to include only relevant ones.
> > >
> > > The replacement was mostly automated with semantic patches like the one
> > > below with manual massaging of format strings.
> > >
> > > @@
> > > expression ptr, size, align;
> > > @@
> > > ptr = memblock_alloc(size, align);
> > > + if (!ptr)
> > > +       panic("%s: Failed to allocate %lu bytes align=0x%lx\n", __func__,
> > > size, align);
> > >
> > > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > > Reviewed-by: Guo Ren <ren_guo@xxxxxxxxx>             # c-sky
> > > Acked-by: Paul Burton <paul.burton@xxxxxxxx>           # MIPS
> > > Acked-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx> # s390
> > > Reviewed-by: Juergen Gross <jgross@xxxxxxxx>         # Xen
> > > ---
> > [...]
> >
> > > diff --git a/mm/sparse.c b/mm/sparse.c
> > > index 7ea5dc6..ad94242 100644
> > > --- a/mm/sparse.c
> > > +++ b/mm/sparse.c
> > [...]
> >
> > > @@ -425,6 +436,10 @@ static void __init sparse_buffer_init(unsigned long size, 
> > > int nid)
> > >                 memblock_alloc_try_nid_raw(size, PAGE_SIZE,
> > >                                                 __pa(MAX_DMA_ADDRESS),
> > >                                                 MEMBLOCK_ALLOC_ACCESSIBLE, nid);
> > > +       if (!sparsemap_buf)
> > > +               panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d 
> > > from=%lx\n",
> > > +                     __func__, size, PAGE_SIZE, nid, __pa(MAX_DMA_ADDRESS));
> > > +
> > memblock_alloc_try_nid_raw() does not panic (help explicitly says: Does not
> > zero allocated memory, does not panic if request cannot be satisfied.).
> "Does not panic" does not mean it always succeeds.
I agree, but at least here you are changing the behaviour by making it 
panic explicitly. Are we sure there are not cases where the system could 
just continue functionning ? Maybe a WARN_ON() would be enough there ?
Christophe

>   
> > Stephen Rothwell reports a boot failure due to this change.
> Please see my reply on that thread.
>
> > Christophe
> >
> > >         sparsemap_buf_end = sparsemap_buf + size;
> > >   }
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