From 8e7f37f2aaa56b723a24f6872817cf9c6410b613 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 7 Dec 2020 17:41:02 -0800 Subject: mm: Add mem_dump_obj() to print source of memory block There are kernel facilities such as per-CPU reference counts that give error messages in generic handlers or callbacks, whose messages are unenlightening. In the case of per-CPU reference-count underflow, this is not a problem when creating a new use of this facility because in that case the bug is almost certainly in the code implementing that new use. However, trouble arises when deploying across many systems, which might exercise corner cases that were not seen during development and testing. Here, it would be really nice to get some kind of hint as to which of several uses the underflow was caused by. This commit therefore exposes a mem_dump_obj() function that takes a pointer to memory (which must still be allocated if it has been dynamically allocated) and prints available information on where that memory came from. This pointer can reference the middle of the block as well as the beginning of the block, as needed by things like RCU callback functions and timer handlers that might not know where the beginning of the memory block is. These functions and handlers can use mem_dump_obj() to print out better hints as to where the problem might lie. The information printed can depend on kernel configuration. For example, the allocation return address can be printed only for slab and slub, and even then only when the necessary debug has been enabled. For slab, build with CONFIG_DEBUG_SLAB=y, and either use sizes with ample space to the next power of two or use the SLAB_STORE_USER when creating the kmem_cache structure. For slub, build with CONFIG_SLUB_DEBUG=y and boot with slub_debug=U, or pass SLAB_STORE_USER to kmem_cache_create() if more focused use is desired. Also for slub, use CONFIG_STACKTRACE to enable printing of the allocation-time stack trace. Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andrew Morton Cc: Reported-by: Andrii Nakryiko [ paulmck: Convert to printing and change names per Joonsoo Kim. ] [ paulmck: Move slab definition per Stephen Rothwell and kbuild test robot. ] [ paulmck: Handle CONFIG_MMU=n case where vmalloc() is kmalloc(). ] [ paulmck: Apply Vlastimil Babka feedback on slab.c kmem_provenance(). ] [ paulmck: Extract more info from !SLUB_DEBUG per Joonsoo Kim. ] [ paulmck: Explicitly check for small pointers per Naresh Kamboju. ] Acked-by: Joonsoo Kim Acked-by: Vlastimil Babka Tested-by: Naresh Kamboju Signed-off-by: Paul E. McKenney --- mm/slab_common.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) (limited to 'mm/slab_common.c') diff --git a/mm/slab_common.c b/mm/slab_common.c index e981c80d216c..adbace4256ef 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -537,6 +537,81 @@ bool slab_is_available(void) return slab_state >= UP; } +/** + * kmem_valid_obj - does the pointer reference a valid slab object? + * @object: pointer to query. + * + * Return: %true if the pointer is to a not-yet-freed object from + * kmalloc() or kmem_cache_alloc(), either %true or %false if the pointer + * is to an already-freed object, and %false otherwise. + */ +bool kmem_valid_obj(void *object) +{ + struct page *page; + + /* Some arches consider ZERO_SIZE_PTR to be a valid address. */ + if (object < (void *)PAGE_SIZE || !virt_addr_valid(object)) + return false; + page = virt_to_head_page(object); + return PageSlab(page); +} + +/** + * kmem_dump_obj - Print available slab provenance information + * @object: slab object for which to find provenance information. + * + * This function uses pr_cont(), so that the caller is expected to have + * printed out whatever preamble is appropriate. The provenance information + * depends on the type of object and on how much debugging is enabled. + * For a slab-cache object, the fact that it is a slab object is printed, + * and, if available, the slab name, return address, and stack trace from + * the allocation of that object. + * + * This function will splat if passed a pointer to a non-slab object. + * If you are not sure what type of object you have, you should instead + * use mem_dump_obj(). + */ +void kmem_dump_obj(void *object) +{ + char *cp = IS_ENABLED(CONFIG_MMU) ? "" : "/vmalloc"; + int i; + struct page *page; + unsigned long ptroffset; + struct kmem_obj_info kp = { }; + + if (WARN_ON_ONCE(!virt_addr_valid(object))) + return; + page = virt_to_head_page(object); + if (WARN_ON_ONCE(!PageSlab(page))) { + pr_cont(" non-slab memory.\n"); + return; + } + kmem_obj_info(&kp, object, page); + if (kp.kp_slab_cache) + pr_cont(" slab%s %s", cp, kp.kp_slab_cache->name); + else + pr_cont(" slab%s", cp); + if (kp.kp_objp) + pr_cont(" start %px", kp.kp_objp); + if (kp.kp_data_offset) + pr_cont(" data offset %lu", kp.kp_data_offset); + if (kp.kp_objp) { + ptroffset = ((char *)object - (char *)kp.kp_objp) - kp.kp_data_offset; + pr_cont(" pointer offset %lu", ptroffset); + } + if (kp.kp_slab_cache && kp.kp_slab_cache->usersize) + pr_cont(" size %u", kp.kp_slab_cache->usersize); + if (kp.kp_ret) + pr_cont(" allocated at %pS\n", kp.kp_ret); + else + pr_cont("\n"); + for (i = 0; i < ARRAY_SIZE(kp.kp_stack); i++) { + if (!kp.kp_stack[i]) + break; + pr_info(" %pS\n", kp.kp_stack[i]); + } +} + #ifndef CONFIG_SLOB /* Create a cache during boot when no slab services are available yet */ void __init create_boot_cache(struct kmem_cache *s, const char *name, -- cgit v1.2.3-70-g09d2