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Subject: Re: UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h in
 4.20-rc1
To:     paulmck@linux.ibm.com
Cc:     "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <dc5e555d-129e-aae8-889d-7b4e82197b3b@c-s.fr>
 <20181109201030.GI4170@linux.ibm.com>
From:   Christophe LEROY <christophe.leroy@c-s.fr>
Message-ID: <9b4e6f39-f36b-06e2-ea96-92dec192edc7@c-s.fr>
Date:   Wed, 14 Nov 2018 15:43:05 +0100
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Le 09/11/2018 à 21:10, Paul E. McKenney a écrit :
> On Fri, Nov 09, 2018 at 06:11:20PM +0100, Christophe LEROY wrote:
>> (Resending due to error in Paul's address)
>>
>> Paul
>>
>> I get the following UBSAN reports in 4.20-rc1 on an MPC8321E
>> (powerpc/book3s/32)
>>
>> I bisected it to 3e31009898699dfc ("rcu: Defer reporting RCU-preempt
>> quiescent states when disabled")
> 
> Fixed by dfdc33585b0a ("rcu: Avoid signed integer overflow in
> rcu_preempt_deferred_qs()") in my -rcu tree and in -next, which I intend
> to push into the next merge window.
> 

Thanks, I confirm it fixes the issue.

Do you intend to push it into 4.20-rc3 or do you mean 4.21 ?

Christophe

> 							Thanx, Paul
> 
>> Thanks
>> Christophe
>>
>> [    4.919995] ================================================================================
>> [    4.928428] UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h:623:28
>> [    4.935198] signed integer overflow:
>> [    4.938766] 0 - -2147483648 cannot be represented in type 'int'
>> [    4.944678] CPU: 0 PID: 119 Comm: mkdir Not tainted
>> 4.19.0-rc1-s3k-dev-00005-g5a60513 #214
>> [    4.952908] Call Trace:
>> [    4.955382] [dec4fd20] [c02cb0d0] ubsan_epilogue+0x18/0x74 (unreliable)
>> [    4.962003] [dec4fd30] [c02cb5e0] handle_overflow+0xd0/0xe0
>> [    4.967588] [dec4fdb0] [c007b424] rcu_preempt_deferred_qs+0xc0/0xc8
>> [    4.973857] [dec4fdd0] [c007be28] rcu_note_context_switch+0x74/0x608
>> [    4.980217] [dec4fe10] [c064b790] __schedule+0x58/0x6e0
>> [    4.985448] [dec4fe50] [c064bfdc] preempt_schedule_common+0x48/0x9c
>> [    4.991717] [dec4fe70] [c01308c8] handle_mm_fault+0x10fc/0x1ecc
>> [    4.997639] [dec4fee0] [c001339c] do_page_fault+0x10c/0x760
>> [    5.003225] [dec4ff40] [c001234c] handle_page_fault+0x14/0x40
>> [    5.008968] --- interrupt: 401 at 0xff9cff8
>> [    5.008968]     LR = 0xfeefd78
>> [    5.016170] ================================================================================
>> [    5.024591] ================================================================================
>> [    5.033005] UBSAN: Undefined behaviour in kernel/rcu/tree_plugin.h:627:28
>> [    5.039775] signed integer overflow:
>> [    5.043342] -2147483648 + -2147483648 cannot be represented in type 'int'
>> [    5.050118] CPU: 0 PID: 119 Comm: mkdir Not tainted
>> 4.19.0-rc1-s3k-dev-00005-g5a60513 #214
>> [    5.058348] Call Trace:
>> [    5.060813] [dec4fd20] [c02cb0d0] ubsan_epilogue+0x18/0x74 (unreliable)
>> [    5.067433] [dec4fd30] [c02cb5e0] handle_overflow+0xd0/0xe0
>> [    5.073014] [dec4fdb0] [c007b408] rcu_preempt_deferred_qs+0xa4/0xc8
>> [    5.079283] [dec4fdd0] [c007be28] rcu_note_context_switch+0x74/0x608
>> [    5.085640] [dec4fe10] [c064b790] __schedule+0x58/0x6e0
>> [    5.090871] [dec4fe50] [c064bfdc] preempt_schedule_common+0x48/0x9c
>> [    5.097139] [dec4fe70] [c01308c8] handle_mm_fault+0x10fc/0x1ecc
>> [    5.103059] [dec4fee0] [c001339c] do_page_fault+0x10c/0x760
>> [    5.108642] [dec4ff40] [c001234c] handle_page_fault+0x14/0x40
>> [    5.114385] --- interrupt: 401 at 0xff9cff8
>> [    5.114385]     LR = 0xfeefd78
>> [    5.121588] ================================================================================
>>