linux-kernel - Strange leases behaviour

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Message-ID: <20090119004646.6b8b4567@zonk.pl>
Date:	Mon, 19 Jan 2009 01:46:46 +0100
From:	Adam Osuchowski <adwol@...k.pl>
To:	linux-kernel@...r.kernel.org
Subject: Strange leases behaviour

Kernel 2.6.28 and such a situation:

- process A obtains read lease on file via fcntl(fd, F_SETLEASE, F_RDLCK).
- while process A holds lease, process B tries to open this file for writing,
  what, of course, leads to block process B on open().
- while process A holds lease and process B waits on open(), process C
  tries to open the same file for reading.

Then, process C also blocks on open(), even though it calls open() only
for reading. Even if process B terminates before process A removes lease,
process C still can't open file for reading. But if process B doesn't try
to open file for writing, process C can open it for reading without any
trobule.

Why there is such a bahaviour? Is it not a bug?

Regards.
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