From 8495f7e6732ed248b648d36439795b42ec650b9e Mon Sep 17 00:00:00 2001 From: Sai Praneeth Prakhya Date: Wed, 25 Sep 2019 16:47:27 -0700 Subject: [PATCH] fork: improve error message for corrupted page tables When a user process exits, the kernel cleans up the mm_struct of the user process and during cleanup, check_mm() checks the page tables of the user process for corruption (E.g: unexpected page flags set/cleared). For corrupted page tables, the error message printed by check_mm() isn't very clear as it prints the loop index instead of page table type (E.g: Resident file mapping pages vs Resident shared memory pages). The loop index in check_mm() is used to index rss_stat[] which represents individual memory type stats. Hence, instead of printing index, print memory type, thereby improving error message. Without patch: -------------- [ 204.836425] mm/pgtable-generic.c:29: bad p4d 0000000089eb4e92(800000025f941467) [ 204.836544] BUG: Bad rss-counter state mm:00000000f75895ea idx:0 val:2 [ 204.836615] BUG: Bad rss-counter state mm:00000000f75895ea idx:1 val:5 [ 204.836685] BUG: non-zero pgtables_bytes on freeing mm: 20480 With patch: ----------- [ 69.815453] mm/pgtable-generic.c:29: bad p4d 0000000084653642(800000025ca37467) [ 69.815872] BUG: Bad rss-counter state mm:00000000014a6c03 type:MM_FILEPAGES val:2 [ 69.815962] BUG: Bad rss-counter state mm:00000000014a6c03 type:MM_ANONPAGES val:5 [ 69.816050] BUG: non-zero pgtables_bytes on freeing mm: 20480 Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so that it matches the other print statement. Link: http://lkml.kernel.org/r/da75b5153f617f4c5739c08ee6ebeb3d19db0fbc.1565123758.git.sai.praneeth.prakhya@intel.com Signed-off-by: Sai Praneeth Prakhya Reviewed-by: Anshuman Khandual Suggested-by: Dave Hansen Acked-by: Michal Hocko Acked-by: Vlastimil Babka Acked-by: Dave Hansen Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mm_types_task.h | 4 ++++ kernel/fork.c | 16 ++++++++++++++-- 2 files changed, 18 insertions(+), 2 deletions(-) diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h index d7016dc..c1bc673 100644 --- a/include/linux/mm_types_task.h +++ b/include/linux/mm_types_task.h @@ -36,6 +36,10 @@ struct vmacache { struct vm_area_struct *vmas[VMACACHE_SIZE]; }; +/* + * When updating this, please also update struct resident_page_types[] in + * kernel/fork.c + */ enum { MM_FILEPAGES, /* Resident file mapping pages */ MM_ANONPAGES, /* Resident anonymous pages */ diff --git a/kernel/fork.c b/kernel/fork.c index 5a0fd51..60763c0 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -125,6 +125,15 @@ int nr_threads; /* The idle threads do not count.. */ static int max_threads; /* tunable limit on nr_threads */ +#define NAMED_ARRAY_INDEX(x) [x] = __stringify(x) + +static const char * const resident_page_types[] = { + NAMED_ARRAY_INDEX(MM_FILEPAGES), + NAMED_ARRAY_INDEX(MM_ANONPAGES), + NAMED_ARRAY_INDEX(MM_SWAPENTS), + NAMED_ARRAY_INDEX(MM_SHMEMPAGES), +}; + DEFINE_PER_CPU(unsigned long, process_counts) = 0; __cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */ @@ -645,12 +654,15 @@ static void check_mm(struct mm_struct *mm) { int i; + BUILD_BUG_ON_MSG(ARRAY_SIZE(resident_page_types) != NR_MM_COUNTERS, + "Please make sure 'struct resident_page_types[]' is updated as well"); + for (i = 0; i < NR_MM_COUNTERS; i++) { long x = atomic_long_read(&mm->rss_stat.count[i]); if (unlikely(x)) - printk(KERN_ALERT "BUG: Bad rss-counter state " - "mm:%p idx:%d val:%ld\n", mm, i, x); + pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n", + mm, resident_page_types[i], x); } if (mm_pgtables_bytes(mm)) -- 2.7.4