Commit bc1bb416 authored by Al Viro's avatar Al Viro
Browse files

generic_perform_write()/iomap_write_actor(): saner logics for short copy 



if we run into a short copy and ->write_end() refuses to advance at all,
use the amount we'd managed to copy for the next iteration to handle.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 90679312

fs/iomap/buffered-io.c

+10 −15
Original line number Diff line number Diff line
@@ -771,10 +771,6 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data, 
		 * Otherwise there's a nasty deadlock on copying from the

		 * same page as we're writing to, without it being marked

		 * up-to-date.

		 *

		 * Not only is this an optimisation, but it is also required

		 * to check that the address is actually valid, when atomic

		 * usercopies are used, below.

		 */

		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {

			status = -EFAULT;
@@ -791,25 +787,24 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data, 


		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);



		copied = iomap_write_end(inode, pos, bytes, copied, page, iomap,

		status = iomap_write_end(inode, pos, bytes, copied, page, iomap,

				srcmap);



		cond_resched();



		iov_iter_advance(i, copied);

		if (unlikely(copied == 0)) {

		if (unlikely(status == 0)) {

			/*

			 * If we were unable to copy any data at all, we must

			 * fall back to a single segment length write.

			 *

			 * If we didn't fallback here, we could livelock

			 * because not all segments in the iov can be copied at

			 * once without a pagefault.

			 * A short copy made iomap_write_end() reject the

			 * thing entirely.  Might be memory poisoning

			 * halfway through, might be a race with munmap,

			 * might be severe memory pressure.

			 */

			bytes = min_t(unsigned long, PAGE_SIZE - offset,

						iov_iter_single_seg_count(i));

			if (copied)

				bytes = copied;

			goto again;

		}

		copied = status;

		iov_iter_advance(i, copied);

		pos += copied;

		written += copied;

		length -= copied;

mm/filemap.c

+9 −15
Original line number Diff line number Diff line
@@ -3642,10 +3642,6 @@ ssize_t generic_perform_write(struct file *file, 
		 * Otherwise there's a nasty deadlock on copying from the

		 * same page as we're writing to, without it being marked

		 * up-to-date.

		 *

		 * Not only is this an optimisation, but it is also required

		 * to check that the address is actually valid, when atomic

		 * usercopies are used, below.

		 */

		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {

			status = -EFAULT;
@@ -3672,24 +3668,22 @@ ssize_t generic_perform_write(struct file *file, 
						page, fsdata);

		if (unlikely(status < 0))

			break;

		copied = status;



		cond_resched();



		iov_iter_advance(i, copied);

		if (unlikely(copied == 0)) {

		if (unlikely(status == 0)) {

			/*

			 * If we were unable to copy any data at all, we must

			 * fall back to a single segment length write.

			 *

			 * If we didn't fallback here, we could livelock

			 * because not all segments in the iov can be copied at

			 * once without a pagefault.

			 * A short copy made ->write_end() reject the

			 * thing entirely.  Might be memory poisoning

			 * halfway through, might be a race with munmap,

			 * might be severe memory pressure.

			 */

			bytes = min_t(unsigned long, PAGE_SIZE - offset,

						iov_iter_single_seg_count(i));

			if (copied)

				bytes = copied;

			goto again;

		}

		copied = status;

		iov_iter_advance(i, copied);

		pos += copied;

		written += copied;