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Mon, 29 Jan 2024 04:49:35 -0500 X-MC-Unique: X_1LCiW7OoeQwPj1VhB6fQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8808688B7A3; Mon, 29 Jan 2024 09:49:34 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.42.28.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id 79BAB492BE2; Mon, 29 Jan 2024 09:49:32 +0000 (UTC) From: David Howells To: Christian Brauner Subject: [PATCH 2/2] netfs: Fix missing zero-length check in unbuffered write Date: Mon, 29 Jan 2024 09:49:19 +0000 Message-ID: <20240129094924.1221977-3-dhowells@redhat.com> In-Reply-To: <20240129094924.1221977-1-dhowells@redhat.com> References: <20240129094924.1221977-1-dhowells@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, v9fs@lists.linux.dev, Dominique Martinet , linux_oss@crudebyte.com, Jeff Layton , linux-kernel@vger.kernel.org, Matthew Wilcox , David Howells , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, netfs@lists.linux.dev, ceph-devel@vger.kernel.org, Eric Van Hensbergen , linux-erofs@lists.ozlabs.org, linux-afs@lists.infradead.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" 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 Link: https://lore.kernel.org/r/ZbQUU6QKmIftKsmo@FV7GG9FTHL/ Signed-off-by: David Howells cc: Dominique Martinet cc: Jeff Layton cc: v9fs@lists.linux.dev cc: linux_oss@crudebyte.com cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org --- fs/netfs/buffered_write.c | 3 +++ fs/netfs/direct_write.c | 5 ++++- 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c index a3059b3168fd..9a0d32e4b422 100644 --- a/fs/netfs/buffered_write.c +++ b/fs/netfs/buffered_write.c @@ -477,6 +477,9 @@ ssize_t netfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from) _enter("%llx,%zx,%llx", iocb->ki_pos, iov_iter_count(from), i_size_read(inode)); + if (!iov_iter_count(from)) + return 0; + if ((iocb->ki_flags & IOCB_DIRECT) || test_bit(NETFS_ICTX_UNBUFFERED, &ictx->flags)) return netfs_unbuffered_write_iter(iocb, from); diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c index 60a40d293c87..bee047e20f5d 100644 --- a/fs/netfs/direct_write.c +++ b/fs/netfs/direct_write.c @@ -139,6 +139,9 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from) _enter("%llx,%zx,%llx", iocb->ki_pos, iov_iter_count(from), i_size_read(inode)); + if (!iov_iter_count(from)) + return 0; + trace_netfs_write_iter(iocb, from); netfs_stat(&netfs_n_rh_dio_write); @@ -146,7 +149,7 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from) if (ret < 0) return ret; ret = generic_write_checks(iocb, from); - if (ret < 0) + if (ret <= 0) goto out; ret = file_remove_privs(file); if (ret < 0)