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Date:   Tue, 5 May 2020 12:01:08 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com
Subject: Re: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino
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On Tue, May 05, 2020 at 11:49:32AM -0700, Jaegeuk Kim wrote:
> How about this?
> 
> From 2a6b0e53e592854306062a2dc35db2d8f79062f2 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@kernel.org>
> Date: Tue, 5 May 2020 11:33:29 -0700
> Subject: [PATCH] f2fs: find a living dentry when finding parent ino
> 
> We need to check any dentry still alive to get parent inode number.
> 
> Suggested-by: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  fs/f2fs/file.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index a0a4413d6083b..95139cb85faca 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -169,9 +169,8 @@ static int get_parent_ino(struct inode *inode, nid_t *pino)
>  {
>  	struct dentry *dentry;
>  
> -	inode = igrab(inode);
> -	dentry = d_find_any_alias(inode);
> -	iput(inode);
> +	/* Need to check if valid dentry still exists. */
> +	dentry = d_find_alias(inode);
>  	if (!dentry)
>  		return 0;
>  

It's fine, but it could use some more explanation.  (What's a "valid dentry"?)
How about the following?

From f8fe7d57eead1423e8548ac7a5ec881d701466a5 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Tue, 5 May 2020 11:41:11 -0700
Subject: [PATCH] f2fs: correctly fix the parent inode number during fsync()

fsync() may be called on a deleted file that's still open.  So when
fsync() tries to set the parent inode number when the inode has
LOST_PINO and i_nlink == 1 (to avoid later checkpoints), it needs to
make sure to get the parent directory via a non-deleted alias.

Also remove the unnecessary igrab() and iput(), as the caller already
holds a reference to the inode.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/f2fs/file.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 6ab8f621a3c5a2..b3069188fd3478 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -165,9 +165,11 @@ static int get_parent_ino(struct inode *inode, nid_t *pino)
 {
 	struct dentry *dentry;
 
-	inode = igrab(inode);
-	dentry = d_find_any_alias(inode);
-	iput(inode);
+	/*
+	 * Make sure to get the non-deleted alias.  The alias associated with
+	 * the open file descriptor being fsync()'ed may be deleted already.
+	 */
+	dentry = d_find_alias(inode);
 	if (!dentry)
 		return 0;
 
-- 
2.26.2