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From:   Huang Jianan <huangjianan@oppo.com>
To:     fuse-devel@lists.sourceforge.net
Cc:     huangjianan@oppo.com, guoweichao@oppo.com, zhangshiming@oppo.com,
        linux-kernel@vger.kernel.org
Subject: [PATCH] fuse: avoid deadlock when write fuse inode
Date:   Tue,  2 Feb 2021 12:08:30 +0800
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We found the following deadlock situations in low memory scenarios:
Thread A                         Thread B
- __writeback_single_inode
 - fuse_write_inode
  - fuse_simple_request
   - __fuse_request_send
    - request_wait_answer
                                 - fuse_dev_splice_read
                                  - fuse_copy_fill
                                   - __alloc_pages_direct_reclaim
                                    - do_shrink_slab
                                     - super_cache_scan
                                      - shrink_dentry_list
                                       - dentry_unlink_inode
                                        - iput_final
                                         - inode_wait_for_writeback

The request and inode processed by Thread A and B are the same, which
causes a deadlock. To avoid this, we remove the __GFP_FS flag when
allocating memory in fuse_copy_fill, so there will be no memory
reclaimation in super_cache_scan.

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
---
 fs/fuse/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 588f8d1240aa..e580b9d04c25 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -721,7 +721,7 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
 			if (cs->nr_segs >= cs->pipe->max_usage)
 				return -EIO;
 
-			page = alloc_page(GFP_HIGHUSER);
+			page = alloc_page(GFP_HIGHUSER & ~__GFP_FS);
 			if (!page)
 				return -ENOMEM;
 
-- 
2.25.1