On 8/6/19 5:05 AM, Sai Praneeth Prakhya wrote: > 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> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> I would also add something like this to reduce risk of breaking it in the future: ----8<---- diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h index d7016dcb245e..a6f83cbe4603 100644 --- a/include/linux/mm_types_task.h +++ b/include/linux/mm_types_task.h @@ -36,6 +36,9 @@ struct vmacache { struct vm_area_struct *vmas[VMACACHE_SIZE]; }; +/* + * When touching this, update also resident_page_types in kernel/fork.c + */ enum { MM_FILEPAGES, /* Resident file mapping pages */ MM_ANONPAGES, /* Resident anonymous pages */