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Date:   Sun, 3 Jan 2021 14:32:34 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Toralf Förster <toralf.foerster@....de>,
        Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        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 1/3/21 1:40 PM, Toralf Förster wrote:
> On 12/30/20 10:05 AM, Toralf Förster wrote:
>> On 12/29/20 11:55 PM, Randy Dunlap wrote:
>>>> 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.
>>
>> My plan was to apply that commit on top of the upcoming 5.10.4 and test
>> that, just waiting in moment for Greg to release the stable version.
>>
> I commit 3644e2d2dda on top of 5.10.4 at my server - no issue so far. I
> did NOT patched my desktop (same stable hardened Gentoo Linux, same
> software and kernel versions) - and there it happened under 5.10.4 too:
> 
> Jan  3 20:54:59 t44 kernel: [126159.494365] UBSAN: shift-out-of-bounds
> in ./include/linux/log2.h:57:13
> Jan  3 20:54:59 t44 kernel: [126159.494371] shift exponent 64 is too
> large for 64-bit type 'long unsigned int'
> Jan  3 20:54:59 t44 kernel: [126159.494378] CPU: 0 PID: 16651 Comm: cc1
> Tainted: G        W       T 5.10.4 #5
> Jan  3 20:54:59 t44 kernel: [126159.494381] Hardware name: LENOVO
> 20AQCTO1WW/20AQCTO1WW, BIOS GJETA4WW (2.54 ) 03/27/2020
> Jan  3 20:54:59 t44 kernel: [126159.494383] Call Trace:
> Jan  3 20:54:59 t44 kernel: [126159.494397]  dump_stack+0x57/0x6a
> Jan  3 20:54:59 t44 kernel: [126159.494402]  ubsan_epilogue+0x5/0x40
> Jan  3 20:54:59 t44 kernel: [126159.494408]
> __ubsan_handle_shift_out_of_bounds.cold+0x61/0x10e
> Jan  3 20:54:59 t44 kernel: [126159.494419]
> ondemand_readahead.cold+0x16/0x21
> Jan  3 20:54:59 t44 kernel: [126159.494427]
> generic_file_buffered_read+0x43d/0x880
> Jan  3 20:54:59 t44 kernel: [126159.494437]  new_sync_read+0x15d/0x1f0
> Jan  3 20:54:59 t44 kernel: [126159.494442]  vfs_read+0xf5/0x190
> Jan  3 20:54:59 t44 kernel: [126159.494447]  ksys_read+0x65/0xe0
> Jan  3 20:54:59 t44 kernel: [126159.494453]  do_syscall_64+0x33/0x40
> Jan  3 20:54:59 t44 kernel: [126159.494460]
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> Jan  3 20:54:59 t44 kernel: [126159.494466] RIP: 0033:0x7feace476dfe
> Jan  3 20:54:59 t44 kernel: [126159.494472] Code: c0 e9 c6 fe ff ff 50
> 48 8d 3d de d6 09 00 e8 89 e4 01 00 66 0f 1f 84 00 00 00 00 00 64 8b 04
> 25 18 00 00 00 85 c0 75 14 0f 05 <48> 3d 00 f0 ff ff 77 5a c3 66 0f 1f
> 84 00 00 00 00 00 48 83 ec 28
> Jan  3 20:54:59 t44 kernel: [126159.494476] RSP: 002b:00007ffe122f4318
> EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> Jan  3 20:54:59 t44 kernel: [126159.494483] RAX: ffffffffffffffda RBX:
> 0000000000000000 RCX: 00007feace476dfe
> Jan  3 20:54:59 t44 kernel: [126159.494486] RDX: 0000000000000000 RSI:
> 00000000047971a0 RDI: 0000000000000008
> Jan  3 20:54:59 t44 kernel: [126159.494489] RBP: 00000000047ba600 R08:
> 00000000047971a0 R09: 000000000470d010
> Jan  3 20:54:59 t44 kernel: [126159.494492] R10: 00007feace543a00 R11:
> 0000000000000246 R12: 0000000004721610
> Jan  3 20:54:59 t44 kernel: [126159.494495] R13: 00000000047971a0 R14:
> 0000000000000000 R15: 0000000000000000
> Jan  3 20:54:59 t44 kernel: [126159.494499]
> ================================================================================

OK, thanks for testing that commit and letting us know.

-- 
~Randy

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