Patchwork ext4: fix the deadlock in mpage_da_map_and_submit()

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Submitter Kazuya Mio
Date Oct. 13, 2011, 7:13 a.m.
Message ID <4E968F8E.5070802@sx.jp.nec.com>
Download mbox | patch
Permalink /patch/119363/
State Accepted
Headers show

Comments

Kazuya Mio - Oct. 13, 2011, 7:13 a.m.
If ext4_jbd2_file_inode() in mpage_da_map_and_submit() fails due to journal
abort, this function returns to caller without unlocking the page.
It leads to the deadlock, and the patch fixes this issue by calling
mpage_da_submit_io().

Signed-off-by: Kazuya Mio <k-mio@sx.jp.nec.com>
---
 fs/ext4/inode.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)
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Theodore Ts'o - Oct. 20, 2011, 11:47 p.m.
On Thu, Oct 13, 2011 at 04:13:18PM +0900, Kazuya Mio wrote:
> If ext4_jbd2_file_inode() in mpage_da_map_and_submit() fails due to journal
> abort, this function returns to caller without unlocking the page.
> It leads to the deadlock, and the patch fixes this issue by calling
> mpage_da_submit_io().
> 
> Signed-off-by: Kazuya Mio <k-mio@sx.jp.nec.com>

Applied, thanks.

This is an area where we should really clean things up next merge
window, though.  I'm a little uneasy that we will potentially write
back some blocks even though the journal has been aborted (we do this
in other error paths, so this isn't a criticism of this patch, just of
the current state of affairs).

The problem mpage_da_submit_io() is the only way we have to unlock the
pages.  In the future we should probably have a separate path to
unlock the pages in case of an error.  We might also want to merge
mpage_da_submit_io() and mpage_da_map_and_submit(), and to also clean
up a number of comments which are out of date.  (For example,
mpage_da_submit_io() no longer uses ext4_writepage().)

						- Ted
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Patch

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 986e238..cd3ccc0 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1475,9 +1475,11 @@  static void mpage_da_map_and_submit(struct mpage_da_data *mpd)
 
 	if (ext4_should_order_data(mpd->inode)) {
 		err = ext4_jbd2_file_inode(handle, mpd->inode);
-		if (err)
+		if (err) {
 			/* This only happens if the journal is aborted */
-			return;
+			mpd->retval = err;
+			goto submit_io;
+		}
 	}
 
 	/*
@@ -2174,11 +2176,12 @@  retry:
 			ret = 0;
 		} else if (ret == MPAGE_DA_EXTENT_TAIL) {
 			/*
-			 * got one extent now try with
-			 * rest of the pages
+			 * Got one extent now try with rest of the pages.
+			 * If mpd.retval is set -EIO, journal is aborted.
+			 * So we don't need to write any more.
 			 */
 			pages_written += mpd.pages_written;
-			ret = 0;
+			ret = mpd.retval;
 			io_done = 1;
 		} else if (wbc->nr_to_write)
 			/*