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From: Jan Kara <jack@suse.cz>
To: <linux-fsdevel@vger.kernel.org>
Cc: yebin <yebin10@huawei.com>, Christoph Hellwig <hch@infradead.org>,
	<linux-block@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
	Jan Kara <jack@suse.cz>
Subject: [PATCH RFC 0/2] Block and buffer invalidation under a filesystem
Date: Tue, 25 Aug 2020 14:05:52 +0200	[thread overview]
Message-ID: <20200825120554.13070-1-jack@suse.cz> (raw)

Hello,

Recently Ye Bin has reported an ext4 crash which he tracked tracked down to a
problem that several places (block_write_full_page(), fallocate(2) on blkdev,
etc.) can invalidate buffers under a live filesystem - block_invalidatepage()
will clear (among other) BH_Mapped flag and following lookup of the buffer_head
will reinitialize it (init_page_buffers()) which among other things clears
bh->b_private fields which then makes jbd2 crash.

I was thinking how to best fix this. block_write_full_page() is easy to deal
with as the invalidation there is just a relict from the past and we don't need
to invalidate pages there at all (patch 1/2). Other cases are more
questionable. In patch 2/2, I have made fallocate(2) on the block device and
discard ioctls bail with EBUSY if there's filesystem mounted because it seems
very weird and problematic to mess with a block device like that under a
filesystem. What do people think? Is anyone aware of a user that would be
broken by this?

There are also other possibilities of fixing this like making
block_invalidatepage() (or rather new ->invalidatepage callback for the
block device) less aggressive so that it does not discard that much state from
buffer_heads. But details of that are not yet clear to me.

Or other possibilities people see to fix this?

								Honza

             reply	other threads:[~2020-08-25 12:06 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-25 12:05 Jan Kara [this message]
2020-08-25 12:05 ` [PATCH RFC 1/2] fs: Don't invalidate page buffers in block_write_full_page() Jan Kara
2020-08-25 12:05 ` [PATCH RFC 2/2] block: Do not discard buffers under a mounted filesystem Jan Kara
2020-08-25 12:16   ` Christoph Hellwig
2020-08-25 14:10     ` Theodore Y. Ts'o
2020-08-25 15:12       ` Jan Kara
2020-08-25 18:41         ` Matthew Wilcox
2020-08-25 18:49           ` Jan Kara
2020-08-25 14:50     ` Jan Kara
2020-08-27  7:16       ` Christoph Hellwig
2020-08-27 21:39         ` Al Viro
2020-08-28  0:07           ` Dave Chinner
2020-08-28  8:10             ` Jan Kara
2020-08-28  8:21     ` Andreas Dilger
2020-08-29  6:40       ` Christoph Hellwig
2020-08-31  7:48         ` Jan Kara

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