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 07:44, Christophe Leroy a écrit :
> 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 ?
Looking more in details, it looks like everything is done to live with 
sparsemap_buf NULL, all functions using it check it so having it NULL 
shouldn't imply a panic I believe, see code below.
static void *sparsemap_buf __meminitdata;
static void *sparsemap_buf_end __meminitdata;

static void __init sparse_buffer_init(unsigned long size, int nid)
{
        WARN_ON(sparsemap_buf); /* forgot to call sparse_buffer_fini()? */
        sparsemap_buf =
                memblock_alloc_try_nid_raw(size, PAGE_SIZE,
                                                __pa(MAX_DMA_ADDRESS),
                                                MEMBLOCK_ALLOC_ACCESSIBLE, nid);
        sparsemap_buf_end = sparsemap_buf + size;
}

static void __init sparse_buffer_fini(void)
{
        unsigned long size = sparsemap_buf_end - sparsemap_buf;

        if (sparsemap_buf && size > 0)
                memblock_free_early(__pa(sparsemap_buf), size);
        sparsemap_buf = NULL;
}

void * __meminit sparse_buffer_alloc(unsigned long size)
{
        void *ptr = NULL;

        if (sparsemap_buf) {
                ptr = PTR_ALIGN(sparsemap_buf, size);
                if (ptr + size > sparsemap_buf_end)
                        ptr = NULL;
                else
                        sparsemap_buf = ptr + size;
        }
        return ptr;
}


Christophe

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