linux-kernel - Re: [PATCH v4 1/5] mm: Provide kernel parameter to allow disabling page init poisoning

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Message-ID: <4d984974-ff16-35e4-76ff-f5e43e5e90da@deltatee.com>
Date:   Fri, 21 Sep 2018 13:41:12 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Pasha Tatashin <Pavel.Tatashin@...rosoft.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Cc:     "mhocko@...e.com" <mhocko@...e.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "jglisse@...hat.com" <jglisse@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 1/5] mm: Provide kernel parameter to allow disabling
 page init poisoning

On 2018-09-21 1:04 PM, Pasha Tatashin wrote:
> 
>> +			pr_err("vm_debug option '%c' unknown. skipped\n",
>> +			       *str);
>> +		}
>> +
>> +		str++;
>> +	}
>> +out:
>> +	if (page_init_poisoning && !__page_init_poisoning)
>> +		pr_warn("Page struct poisoning disabled by kernel command line option 'vm_debug'\n");
> 
> New lines '\n' can be removed, they are not needed for kprintfs.

No, that's not correct.

A printk without a newline termination is not emitted
as output until the next printk call. (To support KERN_CONT).
Therefore removing the '\n' causes a printk to not be printed when it is
called which can cause long delayed messages and subtle problems when
debugging. Always keep the newline in place even though the kernel will
add one for you if it's missing.

Logan