* Re: [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning
2022-02-01 19:29 [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning Waiman Long
@ 2022-02-01 19:34 ` Waiman Long
2022-02-02 6:07 ` Mike Rapoport
2022-02-19 10:27 ` Hector Martin
2 siblings, 0 replies; 4+ messages in thread
From: Waiman Long @ 2022-02-01 19:34 UTC (permalink / raw)
To: Andrew Morton, Kirill A. Shutemov, Ingo Molnar
Cc: linux-mm, linux-kernel, Justin Forbes, Rafael Aquini
On 2/1/22 14:29, Waiman Long wrote:
> The gcc 12 compiler reports a warning on the following code:
>
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
> #ifdef CONFIG_SPARSEMEM_EXTREME
> if (!mem_section)
> return NULL;
> #endif
> :
>
> With CONFIG_SPARSEMEM_EXTREME on, the mem_section definition is
>
> extern struct mem_section **mem_section;
>
> Obviously, mem_section cannot be NULL, but *mem_section can be if memory
> hasn't been allocated for the dynamic mem_section[] array yet. Fix this
> warning by checking for "!*mem_section" instead.
>
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
Sorry, I forgot to add the line
Reported-by: Justin Forbes <jforbes@redhat.com>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> include/linux/mmzone.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index aed44e9b5d89..bd1b19925f3b 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1390,7 +1390,7 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms)
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
> #ifdef CONFIG_SPARSEMEM_EXTREME
> - if (!mem_section)
> + if (!*mem_section)
> return NULL;
> #endif
> if (!mem_section[SECTION_NR_TO_ROOT(nr)])
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning
2022-02-01 19:29 [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning Waiman Long
2022-02-01 19:34 ` Waiman Long
@ 2022-02-02 6:07 ` Mike Rapoport
2022-02-19 10:27 ` Hector Martin
2 siblings, 0 replies; 4+ messages in thread
From: Mike Rapoport @ 2022-02-02 6:07 UTC (permalink / raw)
To: Waiman Long
Cc: Andrew Morton, Kirill A. Shutemov, Ingo Molnar, linux-mm,
linux-kernel, Justin Forbes, Rafael Aquini
On Tue, Feb 01, 2022 at 02:29:24PM -0500, Waiman Long wrote:
> The gcc 12 compiler reports a warning on the following code:
>
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
> #ifdef CONFIG_SPARSEMEM_EXTREME
> if (!mem_section)
> return NULL;
> #endif
> :
>
> With CONFIG_SPARSEMEM_EXTREME on, the mem_section definition is
>
> extern struct mem_section **mem_section;
>
> Obviously, mem_section cannot be NULL, but *mem_section can be if memory
> hasn't been allocated for the dynamic mem_section[] array yet. Fix this
> warning by checking for "!*mem_section" instead.
Hmm, if mem_section cannot be NULL, it means if will be never allocated,
no?
static void __init memory_present(int nid, unsigned long start, unsigned long end)
{
unsigned long pfn;
#ifdef CONFIG_SPARSEMEM_EXTREME
if (unlikely(!mem_section)) {
unsigned long size, align;
size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
align = 1 << (INTERNODE_CACHE_SHIFT);
mem_section = memblock_alloc(size, align);
if (!mem_section)
panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
__func__, size, align);
}
#endif
...
>
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> include/linux/mmzone.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index aed44e9b5d89..bd1b19925f3b 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1390,7 +1390,7 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms)
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
> #ifdef CONFIG_SPARSEMEM_EXTREME
> - if (!mem_section)
> + if (!*mem_section)
> return NULL;
> #endif
> if (!mem_section[SECTION_NR_TO_ROOT(nr)])
> --
> 2.27.0
>
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning
2022-02-01 19:29 [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning Waiman Long
2022-02-01 19:34 ` Waiman Long
2022-02-02 6:07 ` Mike Rapoport
@ 2022-02-19 10:27 ` Hector Martin
2 siblings, 0 replies; 4+ messages in thread
From: Hector Martin @ 2022-02-19 10:27 UTC (permalink / raw)
To: Waiman Long, Andrew Morton, Kirill A. Shutemov, Ingo Molnar,
Stephen Rothwell
Cc: linux-mm, linux-kernel, Justin Forbes, Rafael Aquini
On 02/02/2022 04.29, Waiman Long wrote:
> The gcc 12 compiler reports a warning on the following code:
>
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
> #ifdef CONFIG_SPARSEMEM_EXTREME
> if (!mem_section)
> return NULL;
> #endif
> :
>
> With CONFIG_SPARSEMEM_EXTREME on, the mem_section definition is
>
> extern struct mem_section **mem_section;
>
> Obviously, mem_section cannot be NULL, but *mem_section can be if memory
> hasn't been allocated for the dynamic mem_section[] array yet. Fix this
> warning by checking for "!*mem_section" instead.
>
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> include/linux/mmzone.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index aed44e9b5d89..bd1b19925f3b 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1390,7 +1390,7 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms)
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
> #ifdef CONFIG_SPARSEMEM_EXTREME
> - if (!mem_section)
> + if (!*mem_section)
> return NULL;
> #endif
> if (!mem_section[SECTION_NR_TO_ROOT(nr)])
>
This broke booting on Apple T6000 (M1 Pro; support not yet mainlined)
and it is obviously incorrect. !*mem_section is the same thing as
!mem_section[0], which is always checking element 0 for NULL instead of
the element we're interested in. These machines don't have memory at 0,
fail the spurious check, and crash on early boot.
[ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x612f0240]
[ 0.000000] Linux version
5.17.0-rc4-asahi-next-20220217-00141-g3eb6fdba1573 (marcan@raider)
(aarch64-linux-gnu-gcc (Gentoo 11.2.0 p1) 11.2.0, GNU ld (Gentoo 2.36.1
p1) 2.36.1) #1112 SMP PREEMPT Sat Feb 19 18:01:31 JST 2022
[ 0.000000] random: fast init done
[ 0.000000] Machine model: Apple MacBook Pro (14-inch, M1 Pro, 2021)
[ 0.000000] efi: UEFI not found.
[ 0.000000] earlycon: s5l0 at MMIO32 0x000000039b200000 (options '')
[ 0.000000] printk: bootconsole [s5l0] enabled
[ 0.000000] Unable to handle kernel NULL pointer dereference at
virtual address 0000000000000000
<snip>
[ 0.000000] pc : sparse_init+0x150/0x268
<snip>
Please revert fff3b2a167db5 and edecc06b4d34e.
--
Hector Martin (marcan@marcan.st)
Public Key: https://mrcn.st/pub
^ permalink raw reply [flat|nested] 4+ messages in thread