From 81b0c8713385ce1b1b9058e916edcf9561ad76d6 Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Thu, 29 Jun 2006 02:24:26 -0700 Subject: [PATCH] generic_file_buffered_write(): handle zero-length iovec segments The recent generic_file_write() deadlock fix caused generic_file_buffered_write() to loop inifinitely when presented with a zero-length iovec segment. Fix. Note that this fix deliberately avoids calling ->prepare_write(), ->commit_write() etc with a zero-length write. This is because I don't trust all filesystems to get that right. This is a cautious approach, for 2.6.17.x. For 2.6.18 we should just go ahead and call ->prepare_write() and ->commit_write() with the zero length and fix any broken filesystems. So I'll make that change once this code is stabilised and backported into 2.6.17.x. The reason for preferring to call ->prepare_write() and ->commit_write() with the zero-length segment: a zero-length segment _should_ be sufficiently uncommon that this is the correct way of handling it. We don't want to optimise for poorly-written userspace at the expense of well-written userspace. Cc: "Vladimir V. Saveliev" Cc: Neil Brown Cc: Martin Schwidefsky Cc: Chris Wright Cc: Greg KH Cc: Cc: walt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index 4082b3b3cea7..648f2c0c8e18 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2125,6 +2125,12 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, break; } + if (unlikely(bytes == 0)) { + status = 0; + copied = 0; + goto zero_length_segment; + } + status = a_ops->prepare_write(file, page, offset, offset+bytes); if (unlikely(status)) { loff_t isize = i_size_read(inode); @@ -2154,7 +2160,8 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov, page_cache_release(page); continue; } - if (likely(copied > 0)) { +zero_length_segment: + if (likely(copied >= 0)) { if (!status) status = copied; -- cgit v1.2.1