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Date: Wed, 31 Jan 2024 06:57:23 +0900
From: Dominique Martinet <asmadeus@codewreck.org>
To: David Howells <dhowells@redhat.com>
Cc: Christian Brauner <christian@brauner.io>,
	Eric Van Hensbergen <ericvh@kernel.org>,
	Jeff Layton <jlayton@kernel.org>,
	Matthew Wilcox <willy@infradead.org>, netfs@lists.linux.dev,
	linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org,
	linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs@lists.linux.dev, linux-erofs@lists.ozlabs.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, linux_oss@crudebyte.com
Subject: Re: [PATCH 2/2] netfs: Fix missing zero-length check in unbuffered
 write
Message-ID: <Zblww5O_bRvKx36g@codewreck.org>
References: <20240129094924.1221977-1-dhowells@redhat.com>
 <20240129094924.1221977-3-dhowells@redhat.com>
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In-Reply-To: <20240129094924.1221977-3-dhowells@redhat.com>

David Howells wrote on Mon, Jan 29, 2024 at 09:49:19AM +0000:
> Fix netfs_unbuffered_write_iter() to return immediately if
> generic_write_checks() returns 0, indicating there's nothing to write.
> Note that netfs_file_write_iter() already does this.
> 
> Also, whilst we're at it, put in checks for the size being zero before we
> even take the locks.  Note that generic_write_checks() can still reduce the
> size to zero, so we still need that check.
> 
> Without this, a warning similar to the following is logged to dmesg:
> 
> 	netfs: Zero-sized write [R=1b6da]
> 
> and the syscall fails with EIO, e.g.:
> 
> 	/sbin/ldconfig.real: Writing of cache extension data failed: Input/output error
> 
> This can be reproduced on 9p by:
> 
> 	xfs_io -f -c 'pwrite 0 0' /xfstest.test/foo
> 
> Fixes: 153a9961b551 ("netfs: Implement unbuffered/DIO write support")
> Reported-by: Eric Van Hensbergen <ericvh@kernel.org>
> Link: https://lore.kernel.org/r/ZbQUU6QKmIftKsmo@FV7GG9FTHL/
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Dominique Martinet <asmadeus@codewreck.org>

Thanks!

Tested-by: Dominique Martinet <asmadeus@codewreck.org>

-- 
Dominique Martinet | Asmadeus