Re: [tip:x86/cache 3/3] arch/x86/kernel/cpu/resctrl/rdtgroup.c:1621:5-8: Unneeded variable: "ret". Return " 0" on line 1655

From: Moger, Babu
Date: Wed Jan 24 2024 - 09:58:51 EST

Hi Boris,

On 1/24/24 04:55, Borislav Petkov wrote:
> On Wed, Jan 24, 2024 at 06:31:41PM +0800, kernel test robot wrote:
>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/cache
>> head: 54e35eb8611cce5550d3d7689679b1a91c864f28
>> commit: 54e35eb8611cce5550d3d7689679b1a91c864f28 [3/3] x86/resctrl: Read supported bandwidth sources from CPUID
>> config: x86_64-randconfig-102-20240124 (https://download.01.org/0day-ci/archive/20240124/202401241810.jbd8Ipa1-lkp@xxxxxxxxx/config)
>> compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202401241810.jbd8Ipa1-lkp@xxxxxxxxx/
>>
>> cocci warnings: (new ones prefixed by >>)
>>>> arch/x86/kernel/cpu/resctrl/rdtgroup.c:1621:5-8: Unneeded variable: "ret". Return " 0" on line 1655

Hmm Interesting..

Looking at the code, I see the ret variable is really not required.

The following patch should fix the problem. Let me know if you want me to
send the patch officially. Thanks

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 2b69e560b05f..6057f96df73f 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -1618,7 +1618,6 @@ static int mbm_config_write_domain(struct
rdt_resource *r,
struct rdt_domain *d, u32 evtid, u32 val)
{
struct mon_config_info mon_info = {0};
- int ret = 0;

/*
* Read the current config value first. If both are the same then
@@ -1652,7 +1651,7 @@ static int mbm_config_write_domain(struct
rdt_resource *r,
resctrl_arch_reset_rmid_all(r, d);

out:
- return ret;
+ return 0;
}

static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)

>
> Well, AFAICT, even with the tree checked out at
>
> 92bd5a139033 ("x86/resctrl: Add interface to write mbm_total_bytes_config")
>
> which is the first patch that added this function, ret is unneeded.
>
> But scripts/coccinelle/misc/returnvar.cocci doesn't warn about it then,
> only now that that hunk with the "return -EINVAL;" is removed in the
> patch you're reporting this against.
>
> Lemme add some cocci people to Cc for comment and leave the rest for
> reference.
>
> Thx.
>
>> vim +1621 arch/x86/kernel/cpu/resctrl/rdtgroup.c
>>
>> 92bd5a1390335b Babu Moger 2023-01-13 1616
>> 92bd5a1390335b Babu Moger 2023-01-13 1617 static int mbm_config_write_domain(struct rdt_resource *r,
>> 92bd5a1390335b Babu Moger 2023-01-13 1618 struct rdt_domain *d, u32 evtid, u32 val)
>> 92bd5a1390335b Babu Moger 2023-01-13 1619 {
>> 92bd5a1390335b Babu Moger 2023-01-13 1620 struct mon_config_info mon_info = {0};
>> 92bd5a1390335b Babu Moger 2023-01-13 @1621 int ret = 0;
>> 92bd5a1390335b Babu Moger 2023-01-13 1622
>> 92bd5a1390335b Babu Moger 2023-01-13 1623 /*
>> 92bd5a1390335b Babu Moger 2023-01-13 1624 * Read the current config value first. If both are the same then
>> 92bd5a1390335b Babu Moger 2023-01-13 1625 * no need to write it again.
>> 92bd5a1390335b Babu Moger 2023-01-13 1626 */
>> 92bd5a1390335b Babu Moger 2023-01-13 1627 mon_info.evtid = evtid;
>> 92bd5a1390335b Babu Moger 2023-01-13 1628 mondata_config_read(d, &mon_info);
>> 92bd5a1390335b Babu Moger 2023-01-13 1629 if (mon_info.mon_config == val)
>> 92bd5a1390335b Babu Moger 2023-01-13 1630 goto out;
>> 92bd5a1390335b Babu Moger 2023-01-13 1631
>> 92bd5a1390335b Babu Moger 2023-01-13 1632 mon_info.mon_config = val;
>> 92bd5a1390335b Babu Moger 2023-01-13 1633
>> 92bd5a1390335b Babu Moger 2023-01-13 1634 /*
>> 92bd5a1390335b Babu Moger 2023-01-13 1635 * Update MSR_IA32_EVT_CFG_BASE MSR on one of the CPUs in the
>> 92bd5a1390335b Babu Moger 2023-01-13 1636 * domain. The MSRs offset from MSR MSR_IA32_EVT_CFG_BASE
>> 92bd5a1390335b Babu Moger 2023-01-13 1637 * are scoped at the domain level. Writing any of these MSRs
>> 92bd5a1390335b Babu Moger 2023-01-13 1638 * on one CPU is observed by all the CPUs in the domain.
>> 92bd5a1390335b Babu Moger 2023-01-13 1639 */
>> 92bd5a1390335b Babu Moger 2023-01-13 1640 smp_call_function_any(&d->cpu_mask, mon_event_config_write,
>> 92bd5a1390335b Babu Moger 2023-01-13 1641 &mon_info, 1);
>> 92bd5a1390335b Babu Moger 2023-01-13 1642
>> 92bd5a1390335b Babu Moger 2023-01-13 1643 /*
>> 92bd5a1390335b Babu Moger 2023-01-13 1644 * When an Event Configuration is changed, the bandwidth counters
>> 92bd5a1390335b Babu Moger 2023-01-13 1645 * for all RMIDs and Events will be cleared by the hardware. The
>> 92bd5a1390335b Babu Moger 2023-01-13 1646 * hardware also sets MSR_IA32_QM_CTR.Unavailable (bit 62) for
>> 92bd5a1390335b Babu Moger 2023-01-13 1647 * every RMID on the next read to any event for every RMID.
>> 92bd5a1390335b Babu Moger 2023-01-13 1648 * Subsequent reads will have MSR_IA32_QM_CTR.Unavailable (bit 62)
>> 92bd5a1390335b Babu Moger 2023-01-13 1649 * cleared while it is tracked by the hardware. Clear the
>> 92bd5a1390335b Babu Moger 2023-01-13 1650 * mbm_local and mbm_total counts for all the RMIDs.
>> 92bd5a1390335b Babu Moger 2023-01-13 1651 */
>> 92bd5a1390335b Babu Moger 2023-01-13 1652 resctrl_arch_reset_rmid_all(r, d);
>> 92bd5a1390335b Babu Moger 2023-01-13 1653
>> 92bd5a1390335b Babu Moger 2023-01-13 1654 out:
>> 92bd5a1390335b Babu Moger 2023-01-13 @1655 return ret;
>> 92bd5a1390335b Babu Moger 2023-01-13 1656 }
>> 92bd5a1390335b Babu Moger 2023-01-13 1657
>>
>> :::::: The code at line 1621 was first introduced by commit
>> :::::: 92bd5a1390335bb3cc76bdf1b4356edbc94d408d x86/resctrl: Add interface to write mbm_total_bytes_config
>>
>> :::::: TO: Babu Moger <babu.moger@xxxxxxx>
>> :::::: CC: Borislav Petkov (AMD) <bp@xxxxxxxxx>
>>
>> --
>> 0-DAY CI Kernel Test Service
>> https://github.com/intel/lkp-tests/wiki
>

--
Thanks
Babu Moger