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Commit 994fc28c authored by Zach Brown's avatar Zach Brown Committed by Joel Becker
Browse files

[PATCH] add AOP_TRUNCATED_PAGE, prepend AOP_ to WRITEPAGE_ACTIVATE 



readpage(), prepare_write(), and commit_write() callers are updated to
understand the special return code AOP_TRUNCATED_PAGE in the style of
writepage() and WRITEPAGE_ACTIVATE.  AOP_TRUNCATED_PAGE tells the caller that
the callee has unlocked the page and that the operation should be tried again
with a new page.  OCFS2 uses this to detect and work around a lock inversion in
its aop methods.  There should be no change in behaviour for methods that don't
return AOP_TRUNCATED_PAGE.

WRITEPAGE_ACTIVATE is also prepended with AOP_ for consistency and they are
made enums so that kerneldoc can be used to document their semantics.

Signed-off-by: default avatarZach Brown <zach.brown@oracle.com>
parent 7063fbf2

drivers/block/loop.c

+18 −5
Original line number Diff line number Diff line
@@ -213,7 +213,7 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec, 
	struct address_space_operations *aops = mapping->a_ops;

	pgoff_t index;

	unsigned offset, bv_offs;

	int len, ret = 0;

	int len, ret;



	down(&mapping->host->i_sem);

	index = pos >> PAGE_CACHE_SHIFT;
@@ -232,9 +232,15 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec, 
		page = grab_cache_page(mapping, index);

		if (unlikely(!page))

			goto fail;

		if (unlikely(aops->prepare_write(file, page, offset,

				offset + size)))

		ret = aops->prepare_write(file, page, offset,

					  offset + size);

		if (unlikely(ret)) {

			if (ret == AOP_TRUNCATED_PAGE) {

				page_cache_release(page);

				continue;

			}

			goto unlock;

		}

		transfer_result = lo_do_transfer(lo, WRITE, page, offset,

				bvec->bv_page, bv_offs, size, IV);

		if (unlikely(transfer_result)) {
@@ -251,9 +257,15 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec, 
			kunmap_atomic(kaddr, KM_USER0);

		}

		flush_dcache_page(page);

		if (unlikely(aops->commit_write(file, page, offset,

				offset + size)))

		ret = aops->commit_write(file, page, offset,

					 offset + size);

		if (unlikely(ret)) {

			if (ret == AOP_TRUNCATED_PAGE) {

				page_cache_release(page);

				continue;

			}

			goto unlock;

		}

		if (unlikely(transfer_result))

			goto unlock;

		bv_offs += size;
@@ -264,6 +276,7 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec, 
		unlock_page(page);

		page_cache_release(page);

	}

	ret = 0;

out:

	up(&mapping->host->i_sem);

	return ret;

drivers/block/rd.c

+2 −2
Original line number Diff line number Diff line
@@ -154,7 +154,7 @@ static int ramdisk_commit_write(struct file *file, struct page *page, 


/*

 * ->writepage to the the blockdev's mapping has to redirty the page so that the

 * VM doesn't go and steal it.  We return WRITEPAGE_ACTIVATE so that the VM

 * VM doesn't go and steal it.  We return AOP_WRITEPAGE_ACTIVATE so that the VM

 * won't try to (pointlessly) write the page again for a while.

 *

 * Really, these pages should not be on the LRU at all.
@@ -165,7 +165,7 @@ static int ramdisk_writepage(struct page *page, struct writeback_control *wbc) 
		make_page_uptodate(page);

	SetPageDirty(page);

	if (wbc->for_reclaim)

		return WRITEPAGE_ACTIVATE;

		return AOP_WRITEPAGE_ACTIVATE;

	unlock_page(page);

	return 0;

}

fs/mpage.c

+1 −1
Original line number Diff line number Diff line
@@ -721,7 +721,7 @@ mpage_writepages(struct address_space *mapping, 
						&last_block_in_bio, &ret, wbc,

						page->mapping->a_ops->writepage);

			}

			if (unlikely(ret == WRITEPAGE_ACTIVATE))

			if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))

				unlock_page(page);

			if (ret || (--(wbc->nr_to_write) <= 0))

				done = 1;

include/linux/fs.h

+31 −0
Original line number Diff line number Diff line
@@ -302,6 +302,37 @@ struct iattr { 
 */

#include <linux/quota.h>



/** 

 * enum positive_aop_returns - aop return codes with specific semantics

 *

 * @AOP_WRITEPAGE_ACTIVATE: Informs the caller that page writeback has

 * 			    completed, that the page is still locked, and

 * 			    should be considered active.  The VM uses this hint

 * 			    to return the page to the active list -- it won't

 * 			    be a candidate for writeback again in the near

 * 			    future.  Other callers must be careful to unlock

 * 			    the page if they get this return.  Returned by

 * 			    writepage(); 

 *

 * @AOP_TRUNCATED_PAGE: The AOP method that was handed a locked page has

 *  			unlocked it and the page might have been truncated.

 *  			The caller should back up to acquiring a new page and

 *  			trying again.  The aop will be taking reasonable

 *  			precautions not to livelock.  If the caller held a page

 *  			reference, it should drop it before retrying.  Returned

 *  			by readpage(), prepare_write(), and commit_write().

 *

 * address_space_operation functions return these large constants to indicate

 * special semantics to the caller.  These are much larger than the bytes in a

 * page to allow for functions that return the number of bytes operated on in a

 * given page.

 */



enum positive_aop_returns {

	AOP_WRITEPAGE_ACTIVATE	= 0x80000,

	AOP_TRUNCATED_PAGE	= 0x80001,

};



/*

 * oh the beauties of C type declarations.

 */

include/linux/writeback.h

+0 −6
Original line number Diff line number Diff line
@@ -59,12 +59,6 @@ struct writeback_control { 
	unsigned for_reclaim:1;			/* Invoked from the page allocator */

};



/*

 * ->writepage() return values (make these much larger than a pagesize, in

 * case some fs is returning number-of-bytes-written from writepage)

 */

#define WRITEPAGE_ACTIVATE	0x80000	/* IO was not started: activate page */



/*

 * fs/fs-writeback.c

 */