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xfs: open code end_buffer_async_write in xfs_finish_page_writeback

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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>
This commit is contained in:
Christoph Hellwig 2017-09-02 09:53:41 -07:00 committed by Darrick J. Wong
parent dd60687ee5
commit 8353a814f2
1 changed files with 47 additions and 24 deletions
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71
fs/xfs/xfs_aops.c
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@ -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);
}