On Mon 05-08-19 20:05:27, 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
I like this. On any occasion I am investigating an issue with an rss
inbalance I have to go back to kernel sources to see which pte type that
is.
> Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so
> that it matches the other print statement.
good change as well. Maybe we should also lower the loglevel (in a
separate patch) as well. While this is not nice because we are
apparently leaking memory behind it shouldn't be really critical enough
to jump on normal consoles.
> 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: Michal Hocko <mhocko@xxxxxxxx>
> ---
>
> 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
--
Michal Hocko
SUSE Labs
