Commit 8495f7e6 authored Sep 25, 2019 by Sai Praneeth Prakhya Committed by Linus Torvalds Sep 25, 2019

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 <sai.praneeth.prakhya@intel.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent aadc4e01

include/linux/mm_types_task.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -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 */

kernel/fork.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -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))

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