From: Andrew Morton <akpm@linux-foundation.org>
To: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
dave.hansen@intel.com, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] fork: Improve error message for corrupted page tables
Date: Wed, 31 Jul 2019 15:27:53 -0700 [thread overview]
Message-ID: <20190731152753.b17d9c4418f4bf6815a27ad8@linux-foundation.org> (raw)
In-Reply-To: <20190730221820.7738-1-sai.praneeth.prakhya@intel.com>
On Tue, 30 Jul 2019 15:18:20 -0700 Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> 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). Hence, improve the
> error message so that it's more informative.
>
> 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
Seems useful.
> --- a/include/linux/mm_types_task.h
> +++ b/include/linux/mm_types_task.h
> @@ -44,6 +44,13 @@ enum {
> NR_MM_COUNTERS
> };
>
> +static const char * const resident_page_types[NR_MM_COUNTERS] = {
> + "MM_FILEPAGES",
> + "MM_ANONPAGES",
> + "MM_SWAPENTS",
> + "MM_SHMEMPAGES",
> +};
But please let's not put this in a header file. We're asking the
compiler to put a copy of all of this into every compilation unit which
includes the header. Presumably the compiler is smart enough not to
do that, but it's not good practice.
next prev parent reply other threads:[~2019-07-31 22:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-30 22:18 [PATCH] fork: Improve error message for corrupted page tables Sai Praneeth Prakhya
2019-07-31 22:27 ` Andrew Morton [this message]
2019-07-31 22:36 ` Sai Praneeth Prakhya
2019-08-01 4:20 ` Andrew Morton
2019-08-02 6:46 ` Prakhya, Sai Praneeth
2019-08-05 13:28 ` Vlastimil Babka
2019-08-06 3:09 ` Sai Praneeth Prakhya
2019-08-01 5:48 ` Anshuman Khandual
2019-08-02 6:52 ` Prakhya, Sai Praneeth
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