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From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Cc:     Jaegeuk Kim <jaegeuk@kernel.org>
Subject: [PATCH 1/6] f2fs: call f2fs_balance_fs outside of locked page
Date:   Mon,  9 Dec 2019 14:23:40 -0800
Message-Id: <20191209222345.1078-1-jaegeuk@kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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Otherwise, we can hit deadlock by waiting for the locked page in
move_data_block in GC.

 Thread A                     Thread B
 - do_page_mkwrite
  - f2fs_vm_page_mkwrite
   - lock_page
                              - f2fs_balance_fs
                                  - mutex_lock(gc_mutex)
                               - f2fs_gc
                                - do_garbage_collect
                                 - ra_data_block
                                  - grab_cache_page
   - f2fs_balance_fs
    - mutex_lock(gc_mutex)

Fixes: 39a8695824510 ("f2fs: refactor ->page_mkwrite() flow")
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 fs/f2fs/file.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index e7fcbd8c23f4..6cebc6681487 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -50,7 +50,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 	struct page *page = vmf->page;
 	struct inode *inode = file_inode(vmf->vma->vm_file);
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-	struct dnode_of_data dn = { .node_changed = false };
+	struct dnode_of_data dn;
 	int err;
 
 	if (unlikely(f2fs_cp_error(sbi))) {
@@ -63,6 +63,9 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 		goto err;
 	}
 
+	/* should do out of any locked page */
+	f2fs_balance_fs(sbi, true);
+
 	sb_start_pagefault(inode->i_sb);
 
 	f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
@@ -120,8 +123,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
 out_sem:
 	up_read(&F2FS_I(inode)->i_mmap_sem);
 
-	f2fs_balance_fs(sbi, dn.node_changed);
-
 	sb_end_pagefault(inode->i_sb);
 err:
 	return block_page_mkwrite_return(err);
-- 
2.19.0.605.g01d371f741-goog