linux-kernel - Re: [next] x86: fs/hugetlbfs/inode.c:673:16: error: variable 'm_index' is uninitialized when used here [-Werror,-Wuninitialized]

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Date:   Thu, 25 Aug 2022 09:56:15 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        regressions@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        James Houghton <jthoughton@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Michal Hocko <mhocko@...e.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Peter Xu <peterx@...hat.com>,
        Prakash Sangappa <prakash.sangappa@...cle.com>
Subject: Re: [next] x86: fs/hugetlbfs/inode.c:673:16: error: variable
 'm_index' is uninitialized when used here [-Werror,-Wuninitialized]

On 08/25/22 16:13, Naresh Kamboju wrote:
> The x86_64 and i386 clang builds failed due to these warnings / errors
> on Linux next-20220825.
> 
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> 
> fs/hugetlbfs/inode.c:673:16: error: variable 'm_index' is
> uninitialized when used here [-Werror,-Wuninitialized]
>                                                 m_start, m_index, truncate_op);
>                                                          ^~~~~~~
> fs/hugetlbfs/inode.c:651:26: note: initialize the variable 'm_index'

Thanks!  That really should be 'index' and not 'm_index'.  The variable
m_index was used in a previous version of the code and should have been
deleted.  Depending on the uninitialized value of m_index, this could
cause long delays as the called routine checks the range m_start to m_index.

Andrew, how would you like to address in your tree?  The following patch
can be applied on top of the original (next commit fcc0d3d00d74 "hugetlb:
handle truncate racing with page faults").  Or, I could squash and
resend the original, or resend the entire series.


>From 99aae359c3a744e6718045d2f24b55c84bed4d56 Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@...cle.com>
Date: Thu, 25 Aug 2022 09:49:08 -0700
Subject: [PATCH] hugetlb: fix/remove uninitialized variable in
 remove_inode_hugepages

Code introduced for the routine remove_inode_hugepages by patch "hugetlb:
handle truncate racing with page faults", incorrectly uses a variable
m_index.  This is a remnant from a previous version of the code when
under development.  Use the correct variable 'index' and remove
'm_index' from the routine.

Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 fs/hugetlbfs/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 52d9b390389b..2f1d6da1bafb 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -648,7 +648,7 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 	const pgoff_t start = lstart >> huge_page_shift(h);
 	const pgoff_t end = lend >> huge_page_shift(h);
 	pgoff_t m_end = lm_end >> huge_page_shift(h);
-	pgoff_t m_start, m_index;
+	pgoff_t m_start;
 	struct folio_batch fbatch;
 	struct folio *folio;
 	pgoff_t next, index;
@@ -670,7 +670,7 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 			 * due to a race with fault code.
 			 */
 			freed += fault_lock_inode_indicies(h, inode, mapping,
-						m_start, m_index, truncate_op);
+						m_start, index, truncate_op);
 
 			/*
 			 * Remove folio that was part of folio_batch.
-- 
2.37.1