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Subject: [PATCH 1/4] mm/resource: return real error codes from walk failures
To:     dave@sr71.net
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        dan.j.williams@intel.com, dave.jiang@intel.com, zwisler@kernel.org,
        vishal.l.verma@intel.com, thomas.lendacky@amd.com,
        akpm@linux-foundation.org, mhocko@suse.com,
        linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, ying.huang@intel.com, fengguang.wu@intel.com,
        bp@suse.de, bhelgaas@google.com, baiyaowei@cmss.chinamobile.com,
        tiwai@suse.de
From:   Dave Hansen <dave.hansen@linux.intel.com>
Date:   Wed, 16 Jan 2019 10:19:01 -0800
References: <20190116181859.D1504459@viggo.jf.intel.com>
In-Reply-To: <20190116181859.D1504459@viggo.jf.intel.com>
Message-Id: <20190116181901.CAF85066@viggo.jf.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


From: Dave Hansen <dave.hansen@linux.intel.com>

walk_system_ram_range() can return an error code either becuase *it*
failed, or because the 'func' that it calls returned an error.  The
memory hotplug does the following:

        ret = walk_system_ram_range(..., func);
        if (ret)
		return ret;

and 'ret' makes it out to userspace, eventually.  The problem is,
walk_system_ram_range() failues that result from *it* failing (as
opposed to 'func') return -1.  That leads to a very odd -EPERM (-1)
return code out to userspace.

Make walk_system_ram_range() return -EINVAL for internal failures to
keep userspace less confused.

This return code is compatible with all the callers that I audited.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ross Zwisler <zwisler@kernel.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: linux-nvdimm@lists.01.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: Huang Ying <ying.huang@intel.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>


Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

 b/kernel/resource.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -puN kernel/resource.c~memory-hotplug-walk_system_ram_range-returns-neg-1 kernel/resource.c
--- a/kernel/resource.c~memory-hotplug-walk_system_ram_range-returns-neg-1	2018-12-20 11:48:41.810771934 -0800
+++ b/kernel/resource.c	2018-12-20 11:48:41.814771934 -0800
@@ -375,7 +375,7 @@ static int __walk_iomem_res_desc(resourc
 				 int (*func)(struct resource *, void *))
 {
 	struct resource res;
-	int ret = -1;
+	int ret = -EINVAL;
 
 	while (start < end &&
 	       !find_next_iomem_res(start, end, flags, desc, first_lvl, &res)) {
@@ -453,7 +453,7 @@ int walk_system_ram_range(unsigned long
 	unsigned long flags;
 	struct resource res;
 	unsigned long pfn, end_pfn;
-	int ret = -1;
+	int ret = -EINVAL;
 
 	start = (u64) start_pfn << PAGE_SHIFT;
 	end = ((u64)(start_pfn + nr_pages) << PAGE_SHIFT) - 1;
_