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

[Mike Rapoport <rppt@xxxxxxxxxxxxx>]

On Thu, Jan 31, 2019 at 08:07:29AM +0100, Christophe Leroy wrote:
> 
> 
> 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.

You are right, I'm preparing the fix right now.
 
> 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
> 

-- 
Sincerely yours,
Mike.


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