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ocfs2_inode_lock_tracker as a variant of ocfs2_inode_lock, is used to
prevent deadlock due to recursive lock acquisition.
But this function does not distinguish whether the requested level is EX
or PR.
If a RP lock has been attained, this function will immediately return
success afterwards even an EX lock is requested.
But actually the return value does not mean that the process got a EX
lock, because ocfs2_inode_lock has not been called.
When taking lock levels into account, we face some different situations:
1. no lock is held
In this case, just lock the inode and return 0
2. We are holding a lock
For this situation, things diverges into several cases
wanted holding what to do
ex ex see 2.1 below
ex pr see 2.2 below
pr ex see 2.1 below
pr pr see 2.1 below
2.1 lock level that is been held is compatible
with the wanted level, so no lock action will be tacken.
2.2 Otherwise, an upgrade is needed, but it is forbidden.
Reason why upgrade within a process is forbidden is that lock upgrade
may cause dead lock. The following illustrate how it happens.
process 1 process 2
ocfs2_inode_lock_tracker(ex=0)
<====== ocfs2_inode_lock_tracker(ex=1)
ocfs2_inode_lock_tracker(ex=1)
For the status quo of ocfs2, without this patch, neither a bug nor
end-user impact will be caused because the wrong logic is avoided.
But I'm afraid this generic interface, may be called by other developers
in future and used in this situation.
a process
ocfs2_inode_lock_tracker(ex=0)
ocfs2_inode_lock_tracker(ex=1)
Link: http://lkml.kernel.org/r/20180510053230.17217-1-lchen@suse.com
Signed-off-by: Larry Chen <lchen@suse.com>
Reviewed-by: Gang He <ghe@suse.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <ge.changwei@h3c.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.