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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>
This commit is contained in:
Sai Praneeth Prakhya 2019-09-25 16:47:27 -07:00 committed by Linus Torvalds
parent aadc4e01db
commit 8495f7e673
2 changed files with 18 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/mm_types_task.h
View File

@ -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 */

16
kernel/fork.c
View File

@ -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))