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mm: make snapshotting pages for stable writes a per-bio operation

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Walking a bio's page mappings has proved problematic, so create a new
bio flag to indicate that a bio's data needs to be snapshotted in order
to guarantee stable pages during writeback.  Next, for the one user
(ext3/jbd) of snapshotting, hook all the places where writes can be
initiated without PG_writeback set, and set BIO_SNAP_STABLE there.

We must also flag journal "metadata" bios for stable writeout, since
file data can be written through the journal.  Finally, the
MS_SNAP_STABLE mount flag (only used by ext3) is now superfluous, so get
rid of it.

[[email protected]: rename _submit_bh()'s `flags' to `bio_flags', delobotomize the _submit_bh declaration]
[[email protected]: teeny cleanup]
Signed-off-by: Darrick J. Wong <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Artem Bityutskiy <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: Jens Axboe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Darrick J. Wong 2013-04-29 15:07:25 -07:00 • committed by Linus Torvalds
commit 7136851117
8 changed files with 34 additions and 31 deletions
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25
fs/jbd/commit.c
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@ -162,8 +162,17 @@ static void journal_do_submit_data(struct buffer_head **wbuf, int bufs,
for (i = 0; i < bufs; i++) {
wbuf[i]->b_end_io = end_buffer_write_sync;
/* We use-up our safety reference in submit_bh() */
submit_bh(write_op, wbuf[i]);
/*
* Here we write back pagecache data that may be mmaped. Since
* we cannot afford to clean the page and set PageWriteback
* here due to lock ordering (page lock ranks above transaction
* start), the data can change while IO is in flight. Tell the
* block layer it should bounce the bio pages if stable data
* during write is required.
*
* We use up our safety reference in submit_bh().
*/
_submit_bh(write_op, wbuf[i], 1 << BIO_SNAP_STABLE);
}
}
@ -667,7 +676,17 @@ start_journal_io:
clear_buffer_dirty(bh);
set_buffer_uptodate(bh);
bh->b_end_io = journal_end_buffer_io_sync;
submit_bh(write_op, bh);
/*
* In data=journal mode, here we can end up
* writing pagecache data that might be
* mmapped. Since we can't afford to clean the
* page and set PageWriteback (see the comment
* near the other use of _submit_bh()), the
* data can change while the write is in
* flight. Tell the block layer to bounce the
* bio pages if stable pages are required.
*/
_submit_bh(write_op, bh, 1 << BIO_SNAP_STABLE);
}
cond_resched();