From: Ritesh Harjani <riteshh@linux.ibm.com>
To: Hillf Danton <hdanton@sina.com>
Cc: syzbot <syzbot+82f324bb69744c5f6969@syzkaller.appspotmail.com>,
adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-next@vger.kernel.org,
sfr@canb.auug.org.au, syzkaller-bugs@googlegroups.com,
tytso@mit.edu
Subject: Re: linux-next test error: BUG: using smp_processor_id() in preemptible [ADDR] code: syz-fuzzer/6792
Date: Wed, 3 Jun 2020 15:36:47 +0530 [thread overview]
Message-ID: <20200603100649.BE4A452054@d06av21.portsmouth.uk.ibm.com> (raw)
In-Reply-To: <20200602145256.9236-1-hdanton@sina.com>
On 6/2/20 8:22 PM, Hillf Danton wrote:
>
> Tue, 02 Jun 2020 04:20:16 -0700
>> syzbot found the following crash on:
>>
>> HEAD commit: 0e21d462 Add linux-next specific files for 20200602
>> git tree: linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=127233ee100000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=ecc1aef35f550ee3
>> dashboard link: https://syzkaller.appspot.com/bug?extid=82f324bb69744c5f6969
>> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+82f324bb69744c5f6969@syzkaller.appspotmail.com
>>
>> BUG: using smp_processor_id() in preemptible [00000000] code: syz-fuzzer/6792
>> caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
>
> Fix 42f56b7a4a7d ("ext4: mballoc: introduce pcpu seqcnt for freeing PA
> to improve ENOSPC handling") by redefining discard_pa_seq to be a simple
> regular sequence counter to axe the need of percpu operation.
Why remove percpu seqcnt? IIUC, percpu are much better in case of a
multi-threaded use case which could run and allocate blocks in parallel.
Whereas a updating a simple variable across different cpus may lead to
cacheline bouncing problem.
Since in this case we can very well have a use case of multiple threads
trying to allocate blocks at the same time, so why change this to a
simple seqcnt from percpu seqcnt?
-ritesh
next parent reply other threads:[~2020-06-03 10:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200602145256.9236-1-hdanton@sina.com>
2020-06-03 10:06 ` Ritesh Harjani [this message]
2020-06-02 11:20 linux-next test error: BUG: using smp_processor_id() in preemptible [ADDR] code: syz-fuzzer/6792 syzbot
2020-06-02 12:41 ` Ritesh Harjani
2020-06-12 12:43 ` Ido Schimmel
2020-06-12 13:39 ` Ritesh Harjani
2020-06-12 13:51 ` Ido Schimmel
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