[REGRESSION] "Locked" and "Pss" in /proc/*/smaps are the same

Commit Message

Vlastimil Babka July 3, 2018, 7:36 a.m. UTC

+CC

On 07/01/2018 08:31 PM, Thomas Lindroth wrote:
> While looking around in /proc on my v4.14.52 system I noticed that
> all processes got a lot of "Locked" memory in /proc/*/smaps. A lot
> more memory than a regular user can usually lock with mlock().
> 
> commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (v4.14-rc1) seems
> to have changed the behavior of "Locked".
> 
> commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317
> Author: Daniel Colascione <[e-mail]>
> Date:   Wed Sep 6 16:25:08 2017 -0700
> 
>     mm: add /proc/pid/smaps_rollup
> 
> Before that commit the code was like this. Notice the VM_LOCKED
> check.
> 
> seq_printf(m,
>            "Size:           %8lu kB\n"
>            "Rss:            %8lu kB\n"
>            "Pss:            %8lu kB\n"
>            "Shared_Clean:   %8lu kB\n"
>            "Shared_Dirty:   %8lu kB\n"
>            "Private_Clean:  %8lu kB\n"
>            "Private_Dirty:  %8lu kB\n"
>            "Referenced:     %8lu kB\n"
>            "Anonymous:      %8lu kB\n"
>            "LazyFree:       %8lu kB\n"
>            "AnonHugePages:  %8lu kB\n"
>            "ShmemPmdMapped: %8lu kB\n"
>            "Shared_Hugetlb: %8lu kB\n"
>            "Private_Hugetlb: %7lu kB\n"
>            "Swap:           %8lu kB\n"
>            "SwapPss:        %8lu kB\n"
>            "KernelPageSize: %8lu kB\n"
>            "MMUPageSize:    %8lu kB\n"
>            "Locked:         %8lu kB\n",
>            (vma->vm_end - vma->vm_start) >> 10,
>            mss.resident >> 10,
>            (unsigned long)(mss.pss >> (10 + PSS_SHIFT)),
>            mss.shared_clean  >> 10,
>            mss.shared_dirty  >> 10,
>            mss.private_clean >> 10,
>            mss.private_dirty >> 10,
>            mss.referenced >> 10,
>            mss.anonymous >> 10,
>            mss.lazyfree >> 10,
>            mss.anonymous_thp >> 10,
>            mss.shmem_thp >> 10,
>            mss.shared_hugetlb >> 10,
>            mss.private_hugetlb >> 10,
>            mss.swap >> 10,
>            (unsigned long)(mss.swap_pss >> (10 + PSS_SHIFT)),
>            vma_kernel_pagesize(vma) >> 10,
>            vma_mmu_pagesize(vma) >> 10,
>            (vma->vm_flags & VM_LOCKED) ?
>                 (unsigned long)(mss.pss >> (10 + PSS_SHIFT)) : 0);
> 
> After that commit Locked is now the same as Pss. This looks like a
> mistake.
> 
> seq_printf(m,
>            "Rss:            %8lu kB\n"
>            "Pss:            %8lu kB\n"
>            "Shared_Clean:   %8lu kB\n"
>            "Shared_Dirty:   %8lu kB\n"
>            "Private_Clean:  %8lu kB\n"
>            "Private_Dirty:  %8lu kB\n"
>            "Referenced:     %8lu kB\n"
>            "Anonymous:      %8lu kB\n"
>            "LazyFree:       %8lu kB\n"
>            "AnonHugePages:  %8lu kB\n"
>            "ShmemPmdMapped: %8lu kB\n"
>            "Shared_Hugetlb: %8lu kB\n"
>            "Private_Hugetlb: %7lu kB\n"
>            "Swap:           %8lu kB\n"
>            "SwapPss:        %8lu kB\n"
>            "Locked:         %8lu kB\n",
>            mss->resident >> 10,
>            (unsigned long)(mss->pss >> (10 + PSS_SHIFT)),
>            mss->shared_clean  >> 10,
>            mss->shared_dirty  >> 10,
>            mss->private_clean >> 10,
>            mss->private_dirty >> 10,
>            mss->referenced >> 10,
>            mss->anonymous >> 10,
>            mss->lazyfree >> 10,
>            mss->anonymous_thp >> 10,
>            mss->shmem_thp >> 10,
>            mss->shared_hugetlb >> 10,
>            mss->private_hugetlb >> 10,
>            mss->swap >> 10,
>            (unsigned long)(mss->swap_pss >> (10 + PSS_SHIFT)),
>            (unsigned long)(mss->pss >> (10 + PSS_SHIFT)));
> 
> The latest git has changed a bit but the functionality is the
> same.

----8<----
From fa721521c981167c24ac8f4be446443d293d741e Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <[e-mail]>
Date: Tue, 3 Jul 2018 09:24:27 +0200
Subject: [PATCH] mm: fix Locked field in /proc/pid/smaps*

Thomas reports:

: While looking around in /proc on my v4.14.52 system I noticed that
: all processes got a lot of "Locked" memory in /proc/*/smaps. A lot
: more memory than a regular user can usually lock with mlock().
:
: commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (v4.14-rc1) seems
: to have changed the behavior of "Locked".
:
: Before that commit the code was like this. Notice the VM_LOCKED
: check.
:
:          (vma->vm_flags & VM_LOCKED) ?
:               (unsigned long)(mss.pss >> (10 + PSS_SHIFT)) : 0);
:
: After that commit Locked is now the same as Pss. This looks like a
: mistake.
:
: (unsigned long)(mss->pss >> (10 + PSS_SHIFT)));

Indeed, the commit has added mss->pss_locked with the correct value that
depends on VM_LOCKED, but forgot to actually use it. Fix it.

Fixes: 493b0e9d945f ("mm: add /proc/pid/smaps_rollup")
Reported-by: Thomas Lindroth <[e-mail]>
Signed-off-by: Vlastimil Babka <[e-mail]>
Cc: [e-mail]
---
 fs/proc/task_mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Vlastimil Babka July 3, 2018, 7:45 a.m. UTC | #1

On 07/03/2018 09:36 AM, Vlastimil Babka wrote:
> On 07/01/2018 08:31 PM, Thomas Lindroth wrote:
>> While looking around in /proc on my v4.14.52 system I noticed that
>> all processes got a lot of "Locked" memory in /proc/*/smaps. A lot
>> more memory than a regular user can usually lock with mlock().
>>
>> commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (v4.14-rc1) seems
>> to have changed the behavior of "Locked".

Oops, I forgot, thanks for the nice report :)

Vlastimil

Daniel Colascione July 3, 2018, 4:20 p.m. UTC | #2

On Tue, Jul 3, 2018 at 12:36 AM, Vlastimil Babka <[e-mail]> wrote:
> +CC
>
> On 07/01/2018 08:31 PM, Thomas Lindroth wrote:
>> While looking around in /proc on my v4.14.52 system I noticed that
>> all processes got a lot of "Locked" memory in /proc/*/smaps. A lot
>> more memory than a regular user can usually lock with mlock().
>>
>> commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (v4.14-rc1) seems
>> to have changed the behavior of "Locked".

Thanks for fixing that. I submitted a patch [1] for this bug and some
others a while ago, but the patch didn't make it into the tree because
or wasn't split up correctly or something, and I had to do other work.

[1] https://marc.info/?l=linux-mm&m=151927723128134&w=2

Vlastimil Babka July 4, 2018, 8:46 a.m. UTC | #3

On 07/03/2018 06:20 PM, Daniel Colascione wrote:
> On Tue, Jul 3, 2018 at 12:36 AM, Vlastimil Babka <[e-mail]> wrote:
>> +CC
>>
>> On 07/01/2018 08:31 PM, Thomas Lindroth wrote:
>>> While looking around in /proc on my v4.14.52 system I noticed that
>>> all processes got a lot of "Locked" memory in /proc/*/smaps. A lot
>>> more memory than a regular user can usually lock with mlock().
>>>
>>> commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (v4.14-rc1) seems
>>> to have changed the behavior of "Locked".
> 
> Thanks for fixing that. I submitted a patch [1] for this bug and some
> others a while ago, but the patch didn't make it into the tree because
> or wasn't split up correctly or something, and I had to do other work.

Hmm I see. I pondered about the patch and wondered if the scenarios it
fixes are really possible for smaps_rollup. Did you observe them in
practice? Namely:
- when seq_file starts and stops multiple times on a single open file
description
- when it issues multiple show calls for the same iterator value

I don't think it can happen when all positions but the last one just
return SEQ_SKIP.

Anyway I think the seq_file iterator API usage for smaps_rollup is
unnecessary. Semantically the file shows only one "element" and that's
the set of rollup values for all vmas. Letting seq_file do the iteration
over vmas brings only complications?

> [1] https://marc.info/?l=linux-mm&m=151927723128134&w=2
>

Patch

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e9679016271f..dfd73a4616ce 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -831,7 +831,8 @@  static int show_smap(struct seq_file *m, void *v, int is_pid)
 		SEQ_PUT_DEC(" kB\nSwap:           ", mss->swap);
 		SEQ_PUT_DEC(" kB\nSwapPss:        ",
 						mss->swap_pss >> PSS_SHIFT);
-		SEQ_PUT_DEC(" kB\nLocked:         ", mss->pss >> PSS_SHIFT);
+		SEQ_PUT_DEC(" kB\nLocked:         ",
+						mss->pss_locked >> PSS_SHIFT);
 		seq_puts(m, " kB\n");
 	}
 	if (!rollup_mode) {