[PATCH] generic_file_buffered_write(): handle zero-length iovec segments (81b0c871) · Commits · 戴 / test

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" <vs@namesys.com> Cc: Neil Brown <neilb@suse.de> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Chris Wright <chrisw@sous-sol.org> Cc: Greg KH <greg@kroah.com> Cc: <stable@kernel.org> Cc: walt <wa1ter@myrealbox.com> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

mm/filemap.c

+8 −1

Original line number	Original line	Diff line number	Diff line
	@@ -2125,6 +2125,12 @@ generic_file_buffered_write(struct kiocb iocb, const struct iovec iov,
	break;		break;
	}		}

			if (unlikely(bytes == 0)) {
			status = 0;
			copied = 0;
			goto zero_length_segment;
			}

	status = a_ops->prepare_write(file, page, offset, offset+bytes);		status = a_ops->prepare_write(file, page, offset, offset+bytes);
	if (unlikely(status)) {		if (unlikely(status)) {
	loff_t isize = i_size_read(inode);		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);		page_cache_release(page);
	continue;		continue;
	}		}
	if (likely(copied > 0)) {		zero_length_segment:
			if (likely(copied >= 0)) {
	if (!status)		if (!status)
	status = copied;		status = copied;

mm/filemap.h

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -88,7 +88,7 @@ filemap_set_next_iovec(const struct iovec *iovp, size_t basep, size_t bytes)
	const struct iovec iov = iovp;		const struct iovec iov = iovp;
	size_t base = *basep;		size_t base = *basep;

	while (bytes) {		do {
	int copy = min(bytes, iov->iov_len - base);		int copy = min(bytes, iov->iov_len - base);

	bytes -= copy;		bytes -= copy;
	@@ -97,7 +97,7 @@ filemap_set_next_iovec(const struct iovec *iovp, size_t basep, size_t bytes)
	iov++;		iov++;
	base = 0;		base = 0;
	}		}
	}		} while (bytes);
	*iovp = iov;		*iovp = iov;
	*basep = base;		*basep = base;
	}		}

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