Hello Andrew,
On 05/11/2018 05:49 AM, Andrew Morton wrote: > On Thu, 10 May 2018 13:32:30 +0800 Larry Chen <lc...@suse.com> wrote: > >> 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) >> > Nice changelog, but it gives no information about the severity of the > bug: how often does it hit and what is the end-user impact. > > This info is needed so that I and others can decide which kernel > version(s) need the patch, so please always include it when fixing a > bug, thanks. Thanks for your review and feel sorry for not providing enough information. 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) By the way, should I resend this patch with this info included? Thanks Larry > _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel
