[Crash-utility] Re: [PATCH] Fix compound_head() and "bt -F" option on Linux 7.1 and later

From: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt; Kernel commit d50569612c29 ("mm: rename the 'compound_head' field in the 'struct page' to 'compound_info'") and related patches [1] changed the field name and its value. Without the patch, crash prints the following warning during startup, WARNING: SLUB: cannot determine how compound pages are linked and "bt -F" option fails with the following error. crash> bt -F bt: invalid structure member offset: page_first_page FILE: memory.c LINE: 20238 FUNCTION: compound_head() [1] https://lore.kernel.org/all/20260227194302.274384-1-kas@kernel.org/ Signed-off-by: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt; --- defs.h | 1 + memory.c | 44 ++++++++++++++++++++++++++++++++++++-------- symbols.c | 1 + 3 files changed, 38 insertions(+), 8 deletions(-) diff --git a/defs.h b/defs.h index e3027e2b9141..88b7bbeb2372 100644 --- a/defs.h +++ b/defs.h @@ -2295,6 +2295,7 @@ struct offset_table { /* stash of commonly-used offsets */ long page_compound_order; long folio__folio_order; long folio__flags_1; + long page_compound_info; }; struct size_table { /* stash of commonly-used sizes */ diff --git a/memory.c b/memory.c index 3f3aa274ab5a..7102e951f1d5 100644 --- a/memory.c +++ b/memory.c @@ -414,6 +414,7 @@ mem_init(void) #define FOLIO_ORDER_V2 2 #define FOLIO_ORDER_V3 3 static int folio_order_version; +static int compound_info_has_mask = FALSE; /* * Stash a few popular offsets and some basic kernel virtual memory @@ -547,6 +548,7 @@ vm_init(void) MEMBER_OFFSET_INIT(page_compound_head, "page", "compound_head"); if (INVALID_MEMBER(page_compound_head)) ANON_MEMBER_OFFSET_INIT(page_compound_head, "page", "compound_head"); + MEMBER_OFFSET_INIT(page_compound_info, "page", "compound_info"); MEMBER_OFFSET_INIT(page_private, "page", "private"); MEMBER_OFFSET_INIT(page_freelist, "page", "freelist"); MEMBER_OFFSET_INIT(page_page_type, "page", "page_type"); @@ -1352,6 +1354,17 @@ vm_init(void) } else if (CRASHDEBUG(1)) error(NOTE, "page_hash_table does not exist in this kernel\n"); + /* + * on Linux 7.1 and later, zone.vmemmap_tails is defined only when + * CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is enabled. + */ +#define is_power_of_2(n) (n - 1 < (n ^ (n - 1)))

+ if (VALID_MEMBER(page_compound_info) && + is_power_of_2(SIZE(page)) && MEMBER_EXISTS("zone", "vmemmap_tails")) + compound_info_has_mask = TRUE; + if (CRASHDEBUG(1)) + error(NOTE, "compound_info_has_mask = %d\n", compound_info_has_mask); + kmem_cache_init(); page_flags_init(); @@ -5642,10 +5655,11 @@ PG_slab_flag_init(void) } } - if (VALID_MEMBER(page_compound_head)) { + if (VALID_MEMBER(page_compound_head) || VALID_MEMBER(page_compound_info)) { if (CRASHDEBUG(2)) fprintf(fp, - "PG_head_tail_mask: (UNUSED): page.compound_head exists!\n"); + "PG_head_tail_mask: (UNUSED): page.compound_head or " + "page.compound_info exists!\n"); } else if (vt->flags & KMALLOC_SLUB) { /* * PG_slab and the following are hardwired for @@ -9858,7 +9872,8 @@ vaddr_to_kmem_cache(ulong vaddr, char *buf, int verbose) &page_flags, sizeof(ulong), "page.flags", FAULT_ON_ERROR); if (!page_slab(page, page_flags)) { - if (((vt->flags & KMALLOC_SLUB) || VALID_MEMBER(page_compound_head)) || + if (((vt->flags & KMALLOC_SLUB) || VALID_MEMBER(page_compound_head) || + VALID_MEMBER(page_compound_info)) || ((vt->flags & KMALLOC_COMMON) && VALID_MEMBER(page_slab) && VALID_MEMBER(page_first_page))) { readmem(compound_head(page)+OFFSET(page_flags), KVADDR, @@ -9873,7 +9888,8 @@ vaddr_to_kmem_cache(ulong vaddr, char *buf, int verbose) if ((vt->flags & KMALLOC_SLUB) || ((vt->flags & KMALLOC_COMMON) && VALID_MEMBER(page_slab) && - (VALID_MEMBER(page_compound_head) || VALID_MEMBER(page_first_page)))) { + (VALID_MEMBER(page_compound_head) || VALID_MEMBER(page_compound_info) || + VALID_MEMBER(page_first_page)))) { readmem(compound_head(page)+OFFSET(page_slab), KVADDR, &cache, sizeof(void *), "page.slab", FAULT_ON_ERROR); @@ -9904,7 +9920,8 @@ is_slab_overload_page(ulong vaddr, ulong *page_head, char *buf) if ((vt->flags & SLAB_OVERLOAD_PAGE) && is_page_ptr(vaddr, NULL) && VALID_MEMBER(page_slab) && - (VALID_MEMBER(page_compound_head) || VALID_MEMBER(page_first_page))) { + (VALID_MEMBER(page_compound_head) || VALID_MEMBER(page_compound_info) || + VALID_MEMBER(page_first_page))) { readmem(compound_head(vaddr)+OFFSET(page_slab), KVADDR, &cache, sizeof(void *), "page.slab", FAULT_ON_ERROR); @@ -9944,7 +9961,8 @@ vaddr_to_slab(ulong vaddr) slab = 0; - if ((vt->flags & KMALLOC_SLUB) || VALID_MEMBER(page_compound_head)) + if ((vt->flags & KMALLOC_SLUB) || VALID_MEMBER(page_compound_head) || + VALID_MEMBER(page_compound_info)) slab = compound_head(page); else if (vt->flags & SLAB_OVERLOAD_PAGE) slab = compound_head(page); @@ -20222,11 +20240,21 @@ get_kmem_cache_child_list(ulong **cache_buf, ulong root) static ulong compound_head(ulong page) { - ulong flags, first_page, compound_head; + ulong flags, first_page, compound_head, info, mask; first_page = page; - if (VALID_MEMBER(page_compound_head)) { + if (VALID_MEMBER(page_compound_info)) { + if (readmem(page + OFFSET(page_compound_info), KVADDR, &info, + sizeof(ulong), "page.compound_info", RETURN_ON_ERROR)) { + if (compound_info_has_mask) { + mask = (info & 1) - 1; + mask |= info; + first_page = page & mask; + } else if (info & 1) + first_page = info - 1; + } + } else if (VALID_MEMBER(page_compound_head)) { if (readmem(page+OFFSET(page_compound_head), KVADDR, &compound_head, sizeof(ulong), "page.compound_head", RETURN_ON_ERROR)) { if (compound_head & 1) diff --git a/symbols.c b/symbols.c index 03511c8cbe8c..2071bdf77819 100644 --- a/symbols.c +++ b/symbols.c @@ -10504,6 +10504,7 @@ dump_offset_table(char *spec, ulong makestruct) OFFSET(page_active)); fprintf(fp, " page_compound_head: %ld\n", OFFSET(page_compound_head)); + fprintf(fp, " page_compound_info: %ld\n", OFFSET(page_compound_info)); fprintf(fp, " page_private: %ld\n", OFFSET(page_private)); fprintf(fp, " page_page_type: %ld\n", OFFSET(page_page_type));