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bh=E9e4N+V8UJ4IwjvpQTzUrpD+e3V9ExGL3fz9H07QHkg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jKYbKSi1W0epzrz/uZ+5uBAwbhXUDj60Xs69d9NzD/+WYBYXm7hc2FwoIwumvrcnV PLtGYGeHjQEn94LzxG5c+ckeveAO8T5XNmteMmvUKSf0l1FDYtM7FudRR6NvAHNQBx JHr00v9zeLs6P3/UsPDS3gFQ/1pfqCu9kOj5ntbPq4LXvh6FBsza/jr2stO1T+ztFI QHF4gKfc6jptIHM+u6mxdUmKv92Lie99oQeorBaI2TnNtseHJ4VYK0RXNje6OP2ixC q4Md4mDX2vybOzenMsvNqr+gJDrnf/w159SCvCE82A8tgDKi/2ku0W1AE4qg7MGTkU gFdB8GaOpInRw== From: SeongJae Park To: Kefeng Wang Cc: syzbot , akpm@linux-foundation.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, sj@kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [damon?] divide error in damon_set_attrs Date: Fri, 26 May 2023 18:54:09 +0000 Message-Id: <20230526185409.92039-1-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 46BDC40014 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: oskiaobyjqsipm35m73czkmzp5qi9htg X-HE-Tag: 1685127253-582838 X-HE-Meta: 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 95uOqbjS 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Kefeng and syzbot, On Fri, 26 May 2023 20:59:12 +0800 Kefeng Wang wrote: > > > On 2023/5/26 19:51, syzbot wrote: > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 44c026a73be8 Linux 6.4-rc3 > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=13a92b31280000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=f389ffdf4e9ba3f0 > > dashboard link: https://syzkaller.appspot.com/bug?extid=841a46899768ec7bec67 > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > userspace arch: i386 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/35f16ee05df7/disk-44c026a7.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/10399498a570/vmlinux-44c026a7.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/5c72201ea4ba/bzImage-44c026a7.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+841a46899768ec7bec67@syzkaller.appspotmail.com > > > > divide error: 0000 [#1] PREEMPT SMP KASAN > > CPU: 1 PID: 13527 Comm: syz-executor.1 Not tainted 6.4.0-rc3-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/28/2023 > > RIP: 0010:damon_nr_accesses_to_accesses_bp mm/damon/core.c:491 [inline] > > RIP: 0010:damon_nr_accesses_for_new_attrs mm/damon/core.c:497 [inline] > > RIP: 0010:damon_update_monitoring_result mm/damon/core.c:506 [inline] > > RIP: 0010:damon_update_monitoring_results mm/damon/core.c:534 [inline] > > RIP: 0010:damon_set_attrs+0x224/0x460 mm/damon/core.c:555 Thank you for finding and reporting this bug! The code of the problem is as below: /* convert nr_accesses to access ratio in bp (per 10,000) */ static unsigned int damon_nr_accesses_to_accesses_bp( unsigned int nr_accesses, struct damon_attrs *attrs) { unsigned int max_nr_accesses = attrs->aggr_interval / attrs->sample_interval; return nr_accesses * 10000 / max_nr_accesses; } The problem can happen when 'aggr_interval' is smaller than 'sample_interval', because 'max_nr_accesses' becomes zero in the case, and resulting in divide by zero. Same problem is in damon_accesses_bp_to_nr_accesses(). > > make aggr_interval great than or equal sample_interval? > > diff --git a/mm/damon/core.c b/mm/damon/core.c > index d9ef62047bf5..6fe1960f3d6b 100644 > --- a/mm/damon/core.c > +++ b/mm/damon/core.c > @@ -525,8 +525,8 @@ static void damon_update_monitoring_results(struct > damon_ctx *ctx, > > /* if any interval is zero, simply forgive conversion */ > if (!old_attrs->sample_interval || !old_attrs->aggr_interval || > - !new_attrs->sample_interval || > - !new_attrs->aggr_interval) > + !new_attrs->sample_interval || !new_attrs->aggr_interval || > + new_attrs->aggr_interval < new_attrs->sample_interval) > return; Nice and effective fix! Nevertheless, I think aggregation interval smaller than sample interval is just a wrong input. How about adding the check in damon_set_attrs()'s already existing attributes validation, like below? --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -580,6 +580,8 @@ int damon_set_attrs(struct damon_ctx *ctx, struct damon_attrs *attrs) return -EINVAL; if (attrs->min_nr_regions > attrs->max_nr_regions) return -EINVAL; + if (attrs->aggr_interval < attrs->sample_interval) + return -EINVAL; damon_update_monitoring_results(ctx, attrs); ctx->attrs = *attrs; Thanks, SJ