| Message ID | 12f4b3dc5254547d12cb6669c45c533e647511fb.1532563124.git.osandov@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | /proc/kcore improvements | expand |
Hello Omar, On 07/26/2018 05:29 AM, Omar Sandoval wrote: > From: Omar Sandoval <osandov@fb.com> > > kclist_add() is only called at init time, so there's no point in > grabbing any locks. We're also going to replace the rwlock with a rwsem, > which we don't want to try grabbing during early boot. > > While we're here, mark kclist_add() with __init so that we'll get a > warning if it's called from non-init code. > > Reviewed-by: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Omar Sandoval <osandov@fb.com> > --- > fs/proc/kcore.c | 7 +++---- > include/linux/kcore.h | 2 +- > 2 files changed, 4 insertions(+), 5 deletions(-) > > diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c > index 66c373230e60..b0b9a76f28d6 100644 > --- a/fs/proc/kcore.c > +++ b/fs/proc/kcore.c > @@ -62,16 +62,15 @@ static LIST_HEAD(kclist_head); > static DEFINE_RWLOCK(kclist_lock); > static int kcore_need_update = 1; > > -void > -kclist_add(struct kcore_list *new, void *addr, size_t size, int type) > +/* This doesn't grab kclist_lock, so it should only be used at init time. */ > +void __init kclist_add(struct kcore_list *new, void *addr, size_t size, > + int type) > { > new->addr = (unsigned long)addr; > new->size = size; > new->type = type; > > - write_lock(&kclist_lock); > list_add_tail(&new->list, &kclist_head); > - write_unlock(&kclist_lock); > } > > static size_t get_kcore_size(int *nphdr, size_t *elf_buflen) > diff --git a/include/linux/kcore.h b/include/linux/kcore.h > index 8de55e4b5ee9..c20f296438fb 100644 > --- a/include/linux/kcore.h > +++ b/include/linux/kcore.h > @@ -35,7 +35,7 @@ struct vmcoredd_node { > }; > > #ifdef CONFIG_PROC_KCORE > -extern void kclist_add(struct kcore_list *, void *, size_t, int type); > +void __init kclist_add(struct kcore_list *, void *, size_t, int type); > #else > static inline > void kclist_add(struct kcore_list *new, void *addr, size_t size, int type) > I have been looking at a problem on arm64 platforms where we are trying to get access to PHYS_OFFSET symbol (which indicates the start of physical RAM) in user-space for determining the start of physical RAM in user-space utilities like 'kexec-tools' (please see [1] and [2] for details). Now, I have a 'kexec-tools' implementation available which can read the PHYS_OFFSET from the VMCOREINFO inside '/proc/kcore', which I plan to publish soon on my github tree. I also see that 'readelf' and 'crash' can read the VMCOREINFO from the '/proc/kcore' properly after this patch: # readelf -a --wide /proc/kcore Displaying notes found at file offset 0x00000778 with length 0x000019b4: Owner Data size Description CORE 0x00000188 NT_PRSTATUS (prstatus structure) CORE 0x00000088 NT_PRPSINFO (prpsinfo structure) CORE 0x00001040 NT_TASKSTRUCT (task structure) VMCOREINFO 0x00000710 Unknown note type: (0x00000000) <..snip..> # crash /root/git/linux/vmlinux vmcore -d31 Elf64_Nhdr: n_namesz: 11 ("VMCOREINFO") n_descsz: 1829 n_type: 0 (unused) OSRELEASE=4.18.0-rc7+ PAGESIZE=65536 SYMBOL(init_uts_ns)=ffff5493078a5428 SYMBOL(node_online_map)=ffff54930789d1c8 SYMBOL(swapper_pg_dir)=ffff549308380000 SYMBOL(_stext)=ffff549306681000 SYMBOL(vmap_area_list)=ffff549307944ee0 SYMBOL(mem_section)=ffff92047fffe400 LENGTH(mem_section)=64 SIZE(mem_section)=16 OFFSET(mem_section.section_mem_map)=0 SIZE(page)=64 SIZE(pglist_data)=6656 SIZE(zone)=1728 SIZE(free_area)=88 SIZE(list_head)=16 SIZE(nodemask_t)=8 OFFSET(page.flags)=0 OFFSET(page._refcount)=52 OFFSET(page.mapping)=24 OFFSET(page.lru)=8 OFFSET(page._mapcount)=48 OFFSET(page.private)=40 OFFSET(page.compound_dtor)=16 OFFSET(page.compound_order)=17 OFFSET(page.compound_head)=8 OFFSET(pglist_data.node_zones)=0 OFFSET(pglist_data.nr_zones)=5984 OFFSET(pglist_data.node_start_pfn)=5992 OFFSET(pglist_data.node_spanned_pages)=6008 OFFSET(pglist_data.node_id)=6016 OFFSET(zone.free_area)=192 OFFSET(zone.vm_stat)=1536 OFFSET(zone.spanned_pages)=96 OFFSET(free_area.free_list)=0 OFFSET(list_head.next)=0 OFFSET(list_head.prev)=8 OFFSET(vmap_area.va_start)=0 OFFSET(vmap_area.list)=48 LENGTH(zone.free_area)=14 SYMBOL(log_buf)=ffff5493078ddc30 SYMBOL(log_buf_len)=ffff5493078ddc28 SYMBOL(log_first_idx)=ffff5493081054ac SYMBOL(clear_idx)=ffff5493081054b8 SYMBOL(log_next_idx)=ffff5493081054a8 SIZE(printk_log)=16 OFFSET(printk_log.ts_nsec)=0 OFFSET(printk_log.len)=8 OFFSET(printk_log.text_len)=10 OFFSET(printk_log.dict_len)=12 LENGTH(free_area.free_list)=5 NUMBER(NR_FREE_PAGES)=0 NUMBER(PG_lru)=5 NUMBER(PG_private)=12 NUMBER(PG_swapcache)=9 NUMBER(PG_swapbacked)=18 NUMBER(PG_slab)=8 NUMBER(PG_hwpoison)=21 NUMBER(PG_head_mask)=32768 NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE)=-129 NUMBER(HUGETLB_PAGE_DTOR)=2 NUMBER(VA_BITS)=48 NUMBER(kimage_voffset)=0xffff5492f5c00000 NUMBER(PHYS_OFFSET)=0xffffee1380000000 CRASHTIME=1532965574 So, for what it is worth: Reviewed-by and Tested-by: Bhupesh Sharma <bhsharma@redhat.com> Thanks, Bhupesh [1] https://www.spinics.net/lists/kexec/msg20842.html [2] https://www.spinics.net/lists/kexec/msg20618.html
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c index 66c373230e60..b0b9a76f28d6 100644 --- a/fs/proc/kcore.c +++ b/fs/proc/kcore.c @@ -62,16 +62,15 @@ static LIST_HEAD(kclist_head); static DEFINE_RWLOCK(kclist_lock); static int kcore_need_update = 1; -void -kclist_add(struct kcore_list *new, void *addr, size_t size, int type) +/* This doesn't grab kclist_lock, so it should only be used at init time. */ +void __init kclist_add(struct kcore_list *new, void *addr, size_t size, + int type) { new->addr = (unsigned long)addr; new->size = size; new->type = type; - write_lock(&kclist_lock); list_add_tail(&new->list, &kclist_head); - write_unlock(&kclist_lock); } static size_t get_kcore_size(int *nphdr, size_t *elf_buflen) diff --git a/include/linux/kcore.h b/include/linux/kcore.h index 8de55e4b5ee9..c20f296438fb 100644 --- a/include/linux/kcore.h +++ b/include/linux/kcore.h @@ -35,7 +35,7 @@ struct vmcoredd_node { }; #ifdef CONFIG_PROC_KCORE -extern void kclist_add(struct kcore_list *, void *, size_t, int type); +void __init kclist_add(struct kcore_list *, void *, size_t, int type); #else static inline void kclist_add(struct kcore_list *new, void *addr, size_t size, int type)