Messages in this thread | | | Date | Tue, 26 Feb 2013 16:20:24 +0000 | From | Al Viro <> | Subject | Re: [PATCH] ima: prevent dead lock when a file is opened for direct io |
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On Wed, Feb 20, 2013 at 04:27:51PM -0500, Mimi Zohar wrote: > Hi Al, > > Are there any negative repercussions to temporarily removing the > o_direct flag in order to calculate the file hash? > > thanks, > > Mimi > ----- > > Files are measured or appraised based on the IMA policy. When a file > in policy is opened for read with the O_DIRECT flag set, a deadlock > occurs due to do_blockdev_direct_IO() taking i_mutex before calling > filemap_write_and_wait_range(). The i_mutex was previously taken in > process_measurement(). This patch temporarily removes the O_DIRECT > flag in order to calculate the hash and restores it once completed.
Why does process_measurement() hold ->i_mutex across that? It really sounds like "we kinda hope no ->read() will take ->i_mutex, oops, at least one case does, umm... let's kludge around a bit and hope no other case shows up".
Locking rules should be documented and they should make sense. You are introducing a new one and it's really convoluted - "no ->read() instance for a regular file shall take ->i_mutex unless it's an O_DIRECT open".
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