vfs: Don't call attach_nobh_buffers() with an empty list
This is a modification of a patch by Bill Pemberton <wfp5p@virginia.edu> nobh_write_end() could call attach_nobh_buffers() with head == NULL. This would result in a trap when attach_nobh_buffers() attempted to access bh->b_this_page. This can be illustrated by running the writev01 testcase from LTP on jfs. This error was introduced by commit 5b41e74a "vfs: fix data leak in nobh_write_end()". That patch did not take into account that if PageMappedToDisk() is true upon entry to nobh_write_begin(), then no buffers will be allocated for the page. In that case, we won't have to worry about a failed write leaving unitialized data in the page. Of course, head != NULL implies !page_has_buffers(page), so no need to test both. Signed-off-by: NDave Kleikamp <shaggy@linux.vnet.ibm.com> Cc: Bill Pemberton <wfp5p@virginia.edu> Cc: Dmitri Monakhov <dmonakhov@openvz.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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