lkml.org 
[lkml]   [2017]   [Sep]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.9 76/78] xfs: open code end_buffer_async_write in xfs_finish_page_writeback
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <hch@lst.de>

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 <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/xfs/xfs_aops.c | 72 ++++++++++++++++++++++++++++++++++++------------------
1 file changed, 48 insertions(+), 24 deletions(-)

--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -90,11 +90,11 @@ 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(
@@ -102,29 +102,45 @@ 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) {
+ mapping_set_error(bvec->bv_page->mapping, -EIO);
+ set_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);
}

/*
@@ -138,8 +154,10 @@ 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;
@@ -160,6 +178,11 @@ xfs_destroy_ioend(

bio_put(bio);
}
+
+ if (unlikely(error && !quiet)) {
+ xfs_err_ratelimited(XFS_I(inode)->i_mount,
+ "writeback error on sector %llu", start);
+ }
}

/*
@@ -427,7 +450,8 @@ 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);
}

\
 
 \ /
  Last update: 2017-09-18 11:19    [W:0.440 / U:0.824 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site