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From: Jan Kara <jack@suse.cz>
To: Jeff Layton <jlayton@kernel.org>
Cc: Ilya Dryomov <idryomov@gmail.com>, ceph-devel@vger.kernel.org
Subject: Hole punch races in Ceph
Date: Thu, 22 Apr 2021 13:15:57 +0200	[thread overview]
Message-ID: <20210422111557.GE26221@quack2.suse.cz> (raw)

Hello,

I'm looking into how Ceph protects against races between page fault and
hole punching (I'm unifying protection for this kind of races among
filesystems) and AFAICT it does not. What I have in mind in particular is a
race like:

CPU1					CPU2

ceph_fallocate()
  ...
  ceph_zero_pagecache_range()
					ceph_filemap_fault()
					  faults in page in the range being
					  punched
  ceph_zero_objects()

And now we have a page in punched range with invalid data. If
ceph_page_mkwrite() manages to squeeze in at the right moment, we might
even associate invalid metadata with the page I'd assume (but I'm not sure
whether this would be harmful). Am I missing something?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

             reply	other threads:[~2021-04-22 11:16 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-22 11:15 Jan Kara [this message]
2021-04-22 11:43 ` Jeff Layton
2021-04-22 12:02   ` Jan Kara
2021-04-22 12:05     ` Jeff Layton

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