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: Borislav Petkov
Date: Wed Jan 24 2024 - 05:56:29 EST

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

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

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette