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Date:   Tue, 11 Feb 2020 16:51:10 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Qian Cai <cai@lca.pw>
Cc:     akpm@linux-foundation.org, elver@google.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] mm/kmemleak: annotate a data race in checksum
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On Tue, Feb 11, 2020 at 11:24:05AM -0500, Qian Cai wrote:
> The value of object->pointer could be accessed concurrently as noticed
> by KCSAN,
> 
>  BUG: KCSAN: data-race in crc32_le_base / do_raw_spin_lock
> 
>  write to 0xffffb0ea683a7d50 of 4 bytes by task 23575 on cpu 12:
>   do_raw_spin_lock+0x114/0x200
>   debug_spin_lock_after at kernel/locking/spinlock_debug.c:91
>   (inlined by) do_raw_spin_lock at kernel/locking/spinlock_debug.c:115
>   _raw_spin_lock+0x40/0x50
>   __handle_mm_fault+0xa9e/0xd00
>   handle_mm_fault+0xfc/0x2f0
>   do_page_fault+0x263/0x6f9
>   page_fault+0x34/0x40
> 
>  read to 0xffffb0ea683a7d50 of 4 bytes by task 839 on cpu 60:
>   crc32_le_base+0x67/0x350
>   crc32_le_base+0x67/0x350:
>   crc32_body at lib/crc32.c:106
>   (inlined by) crc32_le_generic at lib/crc32.c:179
>   (inlined by) crc32_le at lib/crc32.c:197
>   kmemleak_scan+0x528/0xd90
>   update_checksum at mm/kmemleak.c:1172
>   (inlined by) kmemleak_scan at mm/kmemleak.c:1497
>   kmemleak_scan_thread+0xcc/0xfa
>   kthread+0x1e0/0x200
>   ret_from_fork+0x27/0x50
> 
>  Reported by Kernel Concurrency Sanitizer on:
>  CPU: 60 PID: 839 Comm: kmemleak Tainted: G        W    L 5.5.0-next-20200210+ #3
>  Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
> 
> crc32() will dereference object->pointer. If a shattered value was
> returned due to a data race, it will be corrected in the next scan.
> Thus, annotate it as an intentional data race using the data_race()
> macro.
> 
> Signed-off-by: Qian Cai <cai@lca.pw>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>