netfs: fix test for whether we can skip read when writing beyond EOF
commit 827a746f 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 827a746f 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: e1b1240c ("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@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/162391826758.1173366.11794946719301590013.stgit@warthog.procyon.org.uk/ # v2 Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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