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Date:   Mon, 17 Feb 2020 20:23:59 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     <richard@....at>, <gregkh@...uxfoundation.org>,
        <sashal@...nel.org>, <yi.zhang@...wei.com>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <Stable@...r.kernel.org>
Subject: [PATCH 4.4] ubifs: Fix deadlock in concurrent bulk-read and writepage

[ Upstream commit f5de5b83303e61b1f3fb09bd77ce3ac2d7a475f2 ]

In ubifs, concurrent execution of writepage and bulk read on the same file
may cause ABBA deadlock, for example (Reproduce method see Link):

Process A(Bulk-read starts from page4)         Process B(write page4 back)
  vfs_read                                       wb_workfn or fsync
  ...                                            ...
  generic_file_buffered_read                     write_cache_pages
    ubifs_readpage                                 LOCK(page4)

      ubifs_bulk_read                              ubifs_writepage
        LOCK(ui->ui_mutex)                           ubifs_write_inode

	  ubifs_do_bulk_read                           LOCK(ui->ui_mutex)
	    find_or_create_page(alloc page4)                  ↑
	      LOCK(page4)                   <--     ABBA deadlock occurs!

In order to ensure the serialization execution of bulk read, we can't
remove the big lock 'ui->ui_mutex' in ubifs_bulk_read(). Instead, we
allow ubifs_do_bulk_read() to lock page failed by replacing
find_or_create_page(FGP_LOCK) with
pagecache_get_page(FGP_LOCK | FGP_NOWAIT).

Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
Suggested-by: zhangyi (F) <yi.zhang@...wei.com>
Cc: <Stable@...r.kernel.org>
Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
Signed-off-by: Richard Weinberger <richard@....at>
---
 fs/ubifs/file.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index b895af7d8d80..e6d0a7df341d 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -782,8 +782,9 @@ static int ubifs_do_bulk_read(struct ubifs_info *c, struct bu_info *bu,
 
 		if (page_offset > end_index)
 			break;
-		page = find_or_create_page(mapping, page_offset,
-					   GFP_NOFS | __GFP_COLD);
+		page = pagecache_get_page(mapping, page_offset,
+				 FGP_LOCK|FGP_ACCESSED|FGP_CREAT|FGP_NOWAIT,
+				 GFP_NOFS | __GFP_COLD);
 		if (!page)
 			break;
 		if (!PageUptodate(page))
-- 
2.7.4

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