| Message ID | 20220201192924.672675-1-longman@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning | expand |
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)])
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 > >
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.
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)])
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(-)