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netfs: Fix i_size updating

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[ Upstream commit 2e0658940d90a3dc130bb3b7f75bae9f4100e01f ]

Fix the updating of i_size, particularly in regard to the completion of DIO
writes and especially async DIO writes by using a lock.

The bug is triggered occasionally by the generic/207 xfstest as it chucks a
bunch of AIO DIO writes at the filesystem and then checks that fstat()
returns a reasonable st_size as each completes.

The problem is that netfs is trying to do "if new_size > inode->i_size,
update inode->i_size" sort of thing but without a lock around it.

This can be seen with cifs, but shouldn't be seen with kafs because kafs
serialises modification ops on the client whereas cifs sends the requests
to the server as they're generated and lets the server order them.

Fixes: 153a9961b5 ("netfs: Implement unbuffered/DIO write support")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/20250701163852.2171681-11-dhowells@redhat.com
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
David Howells
2025-07-01 17:38:45 +01:00
committed by Greg Kroah-Hartman
parent 9b55b7bdb0
commit 50c86c0945
2 changed files with 8 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
fs/netfs/buffered_write.c
View File

@@ -64,6 +64,7 @@ static void netfs_update_i_size(struct netfs_inode *ctx, struct inode *inode,
return;
}
spin_lock(&inode->i_lock);
i_size_write(inode, pos);
#if IS_ENABLED(CONFIG_FSCACHE)
fscache_update_cookie(ctx->cache, NULL, &pos);
@@ -77,6 +78,7 @@ static void netfs_update_i_size(struct netfs_inode *ctx, struct inode *inode,
DIV_ROUND_UP(pos, SECTOR_SIZE),
inode->i_blocks + add);
}
spin_unlock(&inode->i_lock);
}
/**

8
fs/netfs/direct_write.c
View File

@@ -14,13 +14,17 @@ static void netfs_cleanup_dio_write(struct netfs_io_request *wreq)
struct inode *inode = wreq->inode;
unsigned long long end = wreq->start + wreq->transferred;
if (!wreq->error &&
i_size_read(inode) < end) {
if (wreq->error || end <= i_size_read(inode))
return;
spin_lock(&inode->i_lock);
if (end > i_size_read(inode)) {
if (wreq->netfs_ops->update_i_size)
wreq->netfs_ops->update_i_size(inode, end);
else
i_size_write(inode, end);
}
spin_unlock(&inode->i_lock);
}
/*