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Date:   Tue, 29 Dec 2020 14:55:23 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Toralf Förster <toralf.foerster@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org
Subject: Re: [PATCH -mm] mm: readahead: apply a default readahead size

On 12/29/20 2:23 PM, Matthew Wilcox wrote:
> On Tue, Dec 29, 2020 at 01:26:34PM -0800, Randy Dunlap wrote:
>> UBSAN reports an invalid shift size:
>>
>> mr-fox kernel: UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13
>> mr-fox kernel: shift exponent 64 is too large for 64-bit type 'long unsigned int'
>>
>> Original report:
>> https://lore.kernel.org/lkml/c6e5eb81-680f-dd5c-8a81-62041a5ce50c@gmx.de/
>>
>> Follow-up report:
>> https://lore.kernel.org/lkml/0c283ea9-b446-0e40-6dc8-e9585ae171b4@gmx.de/T/#m9b604660925f9e8a544f7453130c31d083c1e5bb
>>
>>
>> Willy suggested that get_init_ra_size() was being called with a size of 0,
>> which would cause this (instead of some Huge value), so add a check in
>> that function for size == 0, and if 0, default it to 32 (pages).
> 
> No, this is wrong.  'size' in this case is the size of the read.
> And it's zero.  Is this fixed by commit
> 3644e2d2dda78e21edd8f5415b6d7ab03f5f54f3
> 

Toralf, can you test with 5.11-rc1 (or later)?

thanks.
-- 
~Randy

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