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.
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Acked-by: Dave Hansen <dave.hansen@xxxxxxxxx>
Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@xxxxxxxxx>
---
Changes from V1 to V2:
----------------------
1. Move struct definition from header file to fork.c file, so that it won't be
included in every compilation unit. As this struct is used *only* in fork.c,
include the definition in fork.c itself.
2. Index the struct to match respective macros.
3. Mention about print function change in commit message.
kernel/fork.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index d8ae0f1b4148..f34f441c50c0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -125,6 +125,13 @@ int nr_threads; /* The idle threads do not count.. */
static int max_threads; /* tunable limit on nr_threads */
+static const char * const resident_page_types[NR_MM_COUNTERS] = {
+ [MM_FILEPAGES] = "MM_FILEPAGES",
+ [MM_ANONPAGES] = "MM_ANONPAGES",
+ [MM_SWAPENTS] = "MM_SWAPENTS",
+ [MM_SHMEMPAGES] = "MM_SHMEMPAGES",
+};
+
DEFINE_PER_CPU(unsigned long, process_counts) = 0;
__cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
@@ -649,8 +656,8 @@ static void check_mm(struct mm_struct *mm)
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
