linux-kernel - Re: [PATCHv4 2/2] mm: use stack_depot_early

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Message-ID: <6e9e406a-8a94-4e34-9e5e-f4bb3a321b4e@suse.cz>
Date:   Thu, 19 Jan 2023 11:32:36 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Zhaoyang Huang <huangzhaoyang@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ke.wang@...soc.com,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
Subject: Re: [PATCHv4 2/2] mm: use stack_depot_early_init for kmemleak

On 1/19/23 02:22, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> Mirsad report bellow error which caused by stack_depot_init failed in kvcalloc.
> Solve this by having stackdepot use stack_depot_early_init.
> 
> On 1/4/23 17:08, Mirsad Goran Todorovac wrote:
> I hate to bring bad news again, but there seems to be a problem with the output of /sys/kernel/debug/kmemleak:
> 
> [root@...mtodorov ~]# cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffff951c118568b0 (size 16):
> comm "kworker/u12:2", pid 56, jiffies 4294893952 (age 4356.548s)
> hex dump (first 16 bytes):
>     6d 65 6d 73 74 69 63 6b 30 00 00 00 00 00 00 00 memstick0.......
>     backtrace:
> [root@...mtodorov ~]#
> 
> Apparently, backtrace of called functions on the stack is no longer printed with the list of memory leaks.
> This appeared on Lenovo desktop 10TX000VCR, with AlmaLinux 8.7 and BIOS version M22KT49A (11/10/2022)
> and 6.2-rc1 and 6.2-rc2 builds.
> This worked on 6.1 with the same CONFIG_KMEMLEAK=y and MGLRU enabled on a vanilla mainstream kernel
> from Mr. Torvalds' tree. I don't know if this is deliberate feature for some reason or a bug.
> Please find attached the config, lshw and kmemleak output.

I think we could replace the full quote of the report with

Link: https://lore.kernel.org/all/5272a819-ef74-65ff-be61-4d2d567337de@alu.unizg.hr/

also

Fixes: 56a61617dd22 ("mm: use stack_depot for recording kmemleak's backtrace")

(Andrew can do that when picking up, no need to send v5)

> reported-by: Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
> suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

But to be cleaner I'd also suggest Andrew adds the hunk below. The call
to stack_depot_init() becomes no-op after this patch so it's not a bug
to leave it there, but it's just misleading now.

---8<---
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 91dda5c2753a..55dc8b8b0616 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -2095,7 +2095,6 @@ void __init kmemleak_init(void)
 	if (kmemleak_error)
 		return;
 
-	stack_depot_init();
 	jiffies_min_age = msecs_to_jiffies(MSECS_MIN_AGE);
 	jiffies_scan_wait = msecs_to_jiffies(SECS_SCAN_WAIT * 1000);