From 0b969d67682679a839f1df448be6764053b5ec2d Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Sun, 17 Sep 2017 14:06:30 -0700 Subject: [PATCH] xfs: open code end_buffer_async_write in xfs_finish_page_writeback BugLink: http://bugs.launchpad.net/bugs/1718412 commit 8353a814f2518dcfa79a5bb77afd0e7dfa391bb1 upstream. Our loop in xfs_finish_page_writeback, which iterates over all buffer heads in a page and then calls end_buffer_async_write, which also iterates over all buffers in the page to check if any I/O is in flight is not only inefficient, but also potentially dangerous as end_buffer_async_write can cause the page and all buffers to be freed. Replace it with a single loop that does the work of end_buffer_async_write on a per-page basis. Signed-off-by: Christoph Hellwig Reviewed-by: Brian Foster Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong Signed-off-by: Greg Kroah-Hartman Signed-off-by: Seth Forshee --- fs/xfs/xfs_aops.c | 71 +++++++++++++++++++++++++++++++---------------- 1 file changed, 47 insertions(+), 24 deletions(-) diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index 6bf120bb1a17..f9efd67f6fa1 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -85,11 +85,11 @@ xfs_find_bdev_for_inode( * associated buffer_heads, paying attention to the start and end offsets that * we need to process on the page. * - * Landmine Warning: bh->b_end_io() will call end_page_writeback() on the last - * buffer in the IO. Once it does this, it is unsafe to access the bufferhead or - * the page at all, as we may be racing with memory reclaim and it can free both - * the bufferhead chain and the page as it will see the page as clean and - * unused. + * Note that we open code the action in end_buffer_async_write here so that we + * only have to iterate over the buffers attached to the page once. This is not + * only more efficient, but also ensures that we only calls end_page_writeback + * at the end of the iteration, and thus avoids the pitfall of having the page + * and buffers potentially freed after every call to end_buffer_async_write. */ static void xfs_finish_page_writeback( @@ -97,29 +97,44 @@ xfs_finish_page_writeback( struct bio_vec *bvec, int error) { - unsigned int end = bvec->bv_offset + bvec->bv_len - 1; - struct buffer_head *head, *bh, *next; + struct buffer_head *head = page_buffers(bvec->bv_page), *bh = head; + bool busy = false; unsigned int off = 0; - unsigned int bsize; + unsigned long flags; ASSERT(bvec->bv_offset < PAGE_SIZE); ASSERT((bvec->bv_offset & (i_blocksize(inode) - 1)) == 0); - ASSERT(end < PAGE_SIZE); + ASSERT(bvec->bv_offset + bvec->bv_len <= PAGE_SIZE); ASSERT((bvec->bv_len & (i_blocksize(inode) - 1)) == 0); - bh = head = page_buffers(bvec->bv_page); - - bsize = bh->b_size; + local_irq_save(flags); + bit_spin_lock(BH_Uptodate_Lock, &head->b_state); do { - if (off > end) - break; - next = bh->b_this_page; - if (off < bvec->bv_offset) - goto next_bh; - bh->b_end_io(bh, !error); -next_bh: - off += bsize; - } while ((bh = next) != head); + if (off >= bvec->bv_offset && + off < bvec->bv_offset + bvec->bv_len) { + ASSERT(buffer_async_write(bh)); + ASSERT(bh->b_end_io == NULL); + + if (error) { + mark_buffer_write_io_error(bh); + clear_buffer_uptodate(bh); + SetPageError(bvec->bv_page); + } else { + set_buffer_uptodate(bh); + } + clear_buffer_async_write(bh); + unlock_buffer(bh); + } else if (buffer_async_write(bh)) { + ASSERT(buffer_locked(bh)); + busy = true; + } + off += bh->b_size; + } while ((bh = bh->b_this_page) != head); + bit_spin_unlock(BH_Uptodate_Lock, &head->b_state); + local_irq_restore(flags); + + if (!busy) + end_page_writeback(bvec->bv_page); } /* @@ -133,8 +148,10 @@ xfs_destroy_ioend( int error) { struct inode *inode = ioend->io_inode; - struct bio *last = ioend->io_bio; - struct bio *bio, *next; + struct bio *bio = &ioend->io_inline_bio; + struct bio *last = ioend->io_bio, *next; + u64 start = bio->bi_iter.bi_sector; + bool quiet = bio_flagged(bio, BIO_QUIET); for (bio = &ioend->io_inline_bio; bio; bio = next) { struct bio_vec *bvec; @@ -155,6 +172,11 @@ xfs_destroy_ioend( bio_put(bio); } + + if (unlikely(error && !quiet)) { + xfs_err_ratelimited(XFS_I(inode)->i_mount, + "writeback error on sector %llu", start); + } } /* @@ -423,7 +445,8 @@ xfs_start_buffer_writeback( ASSERT(!buffer_delay(bh)); ASSERT(!buffer_unwritten(bh)); - mark_buffer_async_write(bh); + bh->b_end_io = NULL; + set_buffer_async_write(bh); set_buffer_uptodate(bh); clear_buffer_dirty(bh); } -- 2.39.2