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78 lines
2.9 KiB
Diff
78 lines
2.9 KiB
Diff
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From df6099279dc346ec77158d5f52d3176dbd0a1e4c Mon Sep 17 00:00:00 2001
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From: Jan Kara <jack@suse.cz>
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Date: Mon, 04 Jul 2016 10:14:01 -0400
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Subject: [PATCH] ext4: fix deadlock during page writeback
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[ Upstream commit 646caa9c8e196880b41cd3e3d33a2ebc752bdb85 ]
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Commit 06bd3c36a733 (ext4: fix data exposure after a crash) uncovered a
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deadlock in ext4_writepages() which was previously much harder to hit.
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After this commit xfstest generic/130 reproduces the deadlock on small
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filesystems.
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The problem happens when ext4_do_update_inode() sets LARGE_FILE feature
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and marks current inode handle as synchronous. That subsequently results
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in ext4_journal_stop() called from ext4_writepages() to block waiting for
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transaction commit while still holding page locks, reference to io_end,
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and some prepared bio in mpd structure each of which can possibly block
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transaction commit from completing and thus results in deadlock.
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Fix the problem by releasing page locks, io_end reference, and
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submitting prepared bio before calling ext4_journal_stop().
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[ Changed to defer the call to ext4_journal_stop() only if the handle
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is synchronous. --tytso ]
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Change-Id: I724640d96ffaa03e512cd0b48cea056b4030c382
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Reported-and-tested-by: Eryu Guan <eguan@redhat.com>
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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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CC: stable@vger.kernel.org
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Signed-off-by: Jan Kara <jack@suse.cz>
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Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
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---
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diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
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index f472aed..5aa499f 100644
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--- a/fs/ext4/inode.c
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+++ b/fs/ext4/inode.c
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@@ -2554,13 +2554,36 @@
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done = true;
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}
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}
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- ext4_journal_stop(handle);
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+ /*
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+ * Caution: If the handle is synchronous,
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+ * ext4_journal_stop() can wait for transaction commit
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+ * to finish which may depend on writeback of pages to
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+ * complete or on page lock to be released. In that
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+ * case, we have to wait until after after we have
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+ * submitted all the IO, released page locks we hold,
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+ * and dropped io_end reference (for extent conversion
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+ * to be able to complete) before stopping the handle.
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+ */
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+ if (!ext4_handle_valid(handle) || handle->h_sync == 0) {
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+ ext4_journal_stop(handle);
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+ handle = NULL;
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+ }
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/* Submit prepared bio */
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ext4_io_submit(&mpd.io_submit);
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/* Unlock pages we didn't use */
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mpage_release_unused_pages(&mpd, give_up_on_write);
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- /* Drop our io_end reference we got from init */
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- ext4_put_io_end(mpd.io_submit.io_end);
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+ /*
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+ * Drop our io_end reference we got from init. We have
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+ * to be careful and use deferred io_end finishing if
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+ * we are still holding the transaction as we can
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+ * release the last reference to io_end which may end
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+ * up doing unwritten extent conversion.
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+ */
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+ if (handle) {
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+ ext4_put_io_end_defer(mpd.io_submit.io_end);
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+ ext4_journal_stop(handle);
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+ } else
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+ ext4_put_io_end(mpd.io_submit.io_end);
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if (ret == -ENOSPC && sbi->s_journal) {
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/*
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