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

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Date: Wed, 24 Jan 2024 11:55:55 +0100
From: Borislav Petkov <bp@...en8.de>
To: kernel test robot <lkp@...el.com>
Cc: Babu Moger <babu.moger@....com>, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Reinette Chatre <reinette.chatre@...el.com>,
	Julia Lawall <Julia.Lawall@...ia.fr>,
	Nicolas Palix <nicolas.palix@...g.fr>, cocci@...ia.fr
Subject: Re: [tip:x86/cache 3/3]
 arch/x86/kernel/cpu/resctrl/rdtgroup.c:1621:5-8: Unneeded variable: "ret".
 Return "  0" on line 1655

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@intel.com/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@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202401241810.jbd8Ipa1-lkp@intel.com/
> 
> 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@....com>
> :::::: CC: Borislav Petkov (AMD) <bp@...en8.de>
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

-- 
Regards/Gruss,
    Boris.

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