linux-kernel - Re: [PATCH][next] cgroup: Avoid -Wstringop-overflow warnings

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Date:   Thu, 22 Jun 2023 08:09:03 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Steven Price <steven.price@....com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] cgroup: Avoid -Wstringop-overflow warnings

Hi!

On 6/22/23 04:11, Steven Price wrote:
> On 15/06/2023 02:18, Gustavo A. R. Silva wrote:
>> Address the following -Wstringop-overflow warnings seen when
>> built with ARM architecture and aspeed_g4_defconfig configuration
>> (notice that under this configuration CGROUP_SUBSYS_COUNT == 0):
>> kernel/cgroup/cgroup.c:1208:16: warning: 'find_existing_css_set' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
>> kernel/cgroup/cgroup.c:1258:15: warning: 'css_set_hash' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
>> kernel/cgroup/cgroup.c:6089:18: warning: 'css_set_hash' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
>> kernel/cgroup/cgroup.c:6153:18: warning: 'css_set_hash' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
>>
>> These changes are based on commit d20d30ebb199 ("cgroup: Avoid compiler
>> warnings with no subsystems").
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>>   kernel/cgroup/cgroup.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> index cd497b90e11a..1ee76e62eb98 100644
>> --- a/kernel/cgroup/cgroup.c
>> +++ b/kernel/cgroup/cgroup.c
>> @@ -1200,6 +1200,9 @@ static struct css_set *find_css_set(struct css_set *old_cset,
>>   	unsigned long key;
>>   	int ssid;
>>   
>> +	if (!CGROUP_HAS_SUBSYS_CONFIG)
>> +		return NULL;
>> +
>>   	lockdep_assert_held(&cgroup_mutex);
>>   
>>   	/* First see if we already have a cgroup group that matches
>> @@ -6045,6 +6048,9 @@ int __init cgroup_init(void)
>>   	struct cgroup_subsys *ss;
>>   	int ssid;
>>   
>> +	if (!CGROUP_HAS_SUBSYS_CONFIG)
>> +		return -EINVAL;
>> +
>>   	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
>>   	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
>>   	BUG_ON(cgroup_init_cftypes(NULL, cgroup_psi_files));
> 
> This change (which landed in linux-next) causes a boot failure on my
> (arm32) board because the cgroup filesystem isn't created which upsets
> systemd:
> 
> [   11.474767] systemd[1]: Failed to mount tmpfs at /sys/fs/cgroup: No such file or directory
> [   11.489933] systemd[1]: Failed to mount cgroup at /sys/fs/cgroup/systemd: No such file or directory
> [!!!!!!] Failed to mount API filesystems.
> 
> Reverting this commit on the head of linux-next gets the board working
> again.

Thanks for reporting this issue. I'll take a look.

--
Gustavo