From: Jeff Layton jlayton@kernel.org
stable inclusion from stable-5.10.47 commit 0463b49e0239bb04f6ca5d7b697645e1122c30f8 bugzilla: 172973 https://gitee.com/openeuler/kernel/issues/I4DAKB
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 827a746f405d25f79560c7868474aec5aee174e1 upstream.
It's not sufficient to skip reading when the pos is beyond the EOF. There may be data at the head of the page that we need to fill in before the write.
Add a new helper function that corrects and clarifies the logic of when we can skip reads, and have it only zero out the part of the page that won't have data copied in for the write.
Finally, don't set the page Uptodate after zeroing. It's not up to date since the write data won't have been copied in yet.
[DH made the following changes:
- Prefixed the new function with "netfs_".
- Don't call zero_user_segments() for a full-page write.
- Altered the beyond-last-page check to avoid a DIV instruction and got rid of then-redundant zero-length file check. ]
[ Note: this fix is commit 827a746f405d in mainline kernels. The original bug was in ceph, but got lifted into the fs/netfs library for v5.13. This backport should apply to stable kernels v5.10 though v5.12. ]
Fixes: e1b1240c1ff5f ("netfs: Add write_begin helper") Reported-by: Andrew W Elble aweits@rit.edu Signed-off-by: Jeff Layton jlayton@kernel.org Signed-off-by: David Howells dhowells@redhat.com Reviewed-by: Matthew Wilcox (Oracle) willy@infradead.org cc: ceph-devel@vger.kernel.org Link: https://lore.kernel.org/r/20210613233345.113565-1-jlayton@kernel.org/ Link: https://lore.kernel.org/r/162367683365.460125.4467036947364047314.stgit@wart... # v1 Link: https://lore.kernel.org/r/162391826758.1173366.11794946719301590013.stgit@wa... # v2 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
Signed-off-by: Chen Jun chenjun102@huawei.com Acked-by: Weilong Chen chenweilong@huawei.com Signed-off-by: Chen Jun chenjun102@huawei.com --- fs/ceph/addr.c | 54 ++++++++++++++++++++++++++++++++++++++------------ 1 file changed, 41 insertions(+), 13 deletions(-)
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c index 35c83f65475b..8b0507f69c15 100644 --- a/fs/ceph/addr.c +++ b/fs/ceph/addr.c @@ -1302,6 +1302,45 @@ ceph_find_incompatible(struct page *page) return NULL; }
+/** + * prep_noread_page - prep a page for writing without reading first + * @page: page being prepared + * @pos: starting position for the write + * @len: length of write + * + * In some cases, write_begin doesn't need to read at all: + * - full page write + * - file is currently zero-length + * - write that lies in a page that is completely beyond EOF + * - write that covers the the page from start to EOF or beyond it + * + * If any of these criteria are met, then zero out the unwritten parts + * of the page and return true. Otherwise, return false. + */ +static bool skip_page_read(struct page *page, loff_t pos, size_t len) +{ + struct inode *inode = page->mapping->host; + loff_t i_size = i_size_read(inode); + size_t offset = offset_in_page(pos); + + /* Full page write */ + if (offset == 0 && len >= PAGE_SIZE) + return true; + + /* pos beyond last page in the file */ + if (pos - offset >= i_size) + goto zero_out; + + /* write that covers the whole page from start to EOF or beyond it */ + if (offset == 0 && (pos + len) >= i_size) + goto zero_out; + + return false; +zero_out: + zero_user_segments(page, 0, offset, offset + len, PAGE_SIZE); + return true; +} + /* * We are only allowed to write into/dirty the page if the page is * clean, or already dirty within the same snap context. @@ -1315,7 +1354,6 @@ static int ceph_write_begin(struct file *file, struct address_space *mapping, struct ceph_snap_context *snapc; struct page *page = NULL; pgoff_t index = pos >> PAGE_SHIFT; - int pos_in_page = pos & ~PAGE_MASK; int r = 0;
dout("write_begin file %p inode %p page %p %d~%d\n", file, inode, page, (int)pos, (int)len); @@ -1350,19 +1388,9 @@ static int ceph_write_begin(struct file *file, struct address_space *mapping, break; }
- /* - * In some cases we don't need to read at all: - * - full page write - * - write that lies completely beyond EOF - * - write that covers the the page from start to EOF or beyond it - */ - if ((pos_in_page == 0 && len == PAGE_SIZE) || - (pos >= i_size_read(inode)) || - (pos_in_page == 0 && (pos + len) >= i_size_read(inode))) { - zero_user_segments(page, 0, pos_in_page, - pos_in_page + len, PAGE_SIZE); + /* No need to read in some cases */ + if (skip_page_read(page, pos, len)) break; - }
/* * We need to read it. If we get back -EINPROGRESS, then the page was