On 2015/8/5 10:20, Gang He wrote: > Hi Joseph, > > Thank a lot, more one question. > > >>>> >> Hi Gang, >> >> On 2015/8/4 11:21, Gang He wrote: >>> Hi Joseph, >>> >>> Thank for your good explaining, have more one question. >>> >>> >>>>>> >>>> Hi Gang, >>>> On 2015/8/3 17:28, Gang He wrote: >>>>> Hello guys, >>>>> >>>>> I went through OCFS2 journal and JBD2 code, I just have one question as >>>> below, >>>>> If there are some nodes which are running, one node (node A) suddenly >>>> crashes, one another node (node B) will recover node A's journal records. >> But >>>> here looks a problem, if node B ever changed one file, and node A also >>>> changed this same file, then node B will replay these changed meta >>>> buffers, >>>> JBD2 recovery code will memcpy the journal meta buffer to the node B's >>>> memory, this inode's meta buffer will be replaced by node A's journal >> record, >>>> but this inode structure in memory will not be reflected, this will cause >>>> this kind of issue? I feel that my guess should be wrong, since this >>>> problem >> >>>> looks too obvious, but who can help to figure out how to solve this >>>> problem >>>> when a running node try to recover a crashed node's journal. >>>>> >>>> Please note that nodes can update the same inode only after it has got >>>> the cluster lock. And if the lock level is not compatible, it will >>>> downcovert first, which will do the checkpoint. >>>> So I don't think the issue you described really exists. >>> You means, if Node A try to change the same file when Node B is changing >>> (or >> just changed) this file, it must wait until Node B finishes the checkpoint >> for these meta buffers, >>> then, Node A will re-read these meta buffers from the shared disk and gets >> the lock, my understanding is right? if yes, how the inode meta buffer >> reflect the inode structure in the memory? >>> There is a case, if Node A ever read a file, then Node B changes the same >> file and write the journal records to the log file (the meta buffers are not >> flushed to the file system) and crashes, at this moment, Node A is replaying >> the journal records and a user is trying to access/change this file, what >> will happen? the memory inode will be inconsistent with just recovered meta >> buffer? looks a little complicated. >>> >> Node A reads a file (take inode lock, level PR), then Node B changes the >> same file (take inode lock, level EX). Here when Node B takes the inode >> EX lock, Node A should downcovert to NL because PR and EX are incompatible. >> So inode cache in Node A is invalid now. >> And only after recovering Node B successfully, Node A can access the file. >> (Because lock is holding by Node B). > The answer looks reasonable, just one question for how Node A re-get the > file(inode) lock after Node B crashed? > since Node B crashed, it no longer do anything, how Node A re-get the file > cluster lock? base on timeout? or journal recovery of Node B from another > Node (maybe or not maybe Node A), I just doubt that journal records do not > include any DLM lock related information. > As described in the previous mail, though Node B has crashed, but the lockres master still thinks Node B has got the EX lock. Now Node A wants to take the PR lock and it will be blocked. This requires DLM recovery first.
Thanks, Joseph > > Thanks > Gang > >> >>> Thanks >>> Gang >>> >>> >>>> >>>> Thanks >>>> Joseph >>>>> >>>>> Thanks >>>>> Gang > > > . > _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel
