Nick, While visiting some issues in ocfs2_page_mkwrite(), I realized that we're returning 0 to mean "Please try again Mr VM", but the caller of page_mkwrite() now expects VM_FAULT_NOPAGE. This is all due to 56a76f [fs: fix page_mkwrite error cases in core code and btrfs]. In the comment for 56a76f, you state that btrfs is the example but all other filesystems need to be fixed...yet ocfs2, ext4, and gfs2 continue to return 0 or VM_FAULT_SIGBUS. I guess this continues to work because we return the page unlocked (thus triggering the "if (unlikely(!(tmp & VM_FAULT_LOCKED)))" logic). Was this expected to continue to work, or do you consider these filesystems broken until they are updated with the new return codes? Back to the ocfs2 issue. Am I correctly reading the current code that we can safely throw away the page passed in to page_mkwrite() if a pagecache flush has dropped it? Currently, we presume that the page passed in must be the one we make writable. We make a quick check of page->mapping == inode->i_mapping, returning 0 (for "try again") immediately if that's false. But once we get into the meat of our locking and finally lock the page for good, we assume mapping==i_mapping still holds. That obviously breaks when the pagecache gets truncated. At this late stage, we -EINVAL (clearly wrong). It looks hard to lock the page for good high up at our first check of the mapping. Wengang has proposed to simply ignore the page passed into page_mkwrite() and just find_or_create_page() the sucker at the place we're ready to consider it stable. As I see it, the two places that call page_mkwrite() are going to revalidate the pte anyway, and they'll find the newly created page if find_or_create_page() gets a different. Is that safe behavior? Joel -- Life's Little Instruction Book #3 "Watch a sunrise at least once a year." Joel Becker Senior Development Manager Oracle E-mail: joel.becker@xxxxxxxxxx Phone: (650) 506-8127 -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
