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Larry Chen authored
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.comSigned-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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