Hi, Dave On 2014/9/3 9:02, Dave Chinner wrote: > On Tue, Sep 02, 2014 at 05:03:27PM +0800, Xue jiufei wrote: >> Hi, Dave >> On 2014/9/2 7:51, Dave Chinner wrote: >>> On Fri, Aug 29, 2014 at 05:57:22PM +0800, Xue jiufei wrote: >>>> The patch trys to solve one deadlock problem caused by cluster >>>> fs, like ocfs2. And the problem may happen at least in the below >>>> situations: >>>> 1)Receiving a connect message from other nodes, node queues a >>>> work_struct o2net_listen_work. >>>> 2)o2net_wq processes this work and calls sock_alloc() to allocate >>>> memory for a new socket. >>>> 3)It would do direct memory reclaim when available memory is not >>>> enough and trigger the inode cleanup. That inode being cleaned up >>>> is happened to be ocfs2 inode, so call evict()->ocfs2_evict_inode() >>>> ->ocfs2_drop_lock()->dlmunlock()->o2net_send_message_vec(), >>>> and wait for the unlock response from master. >>>> 4)tcp layer received the response, call o2net_data_ready() and >>>> queue sc_rx_work, waiting o2net_wq to process this work. >>>> 5)o2net_wq is a single thread workqueue, it process the work one by >>>> one. Right now it is still doing o2net_listen_work and cannot handle >>>> sc_rx_work. so we deadlock. >>>> >>>> It is impossible to set GFP_NOFS for memory allocation in sock_alloc(). >>>> So we use PF_FSTRANS to avoid the task reentering filesystem when >>>> available memory is not enough. >>>> >>>> Signed-off-by: joyce.xue <xuejiufei@xxxxxxxxxx> >>> >>> For the second time: use memalloc_noio_save/memalloc_noio_restore. >>> And please put a great big comment in the code explaining why you >>> need to do this special thing with memory reclaim flags. >>> >>> Cheers, >>> >>> Dave. >>> >> Thanks for your reply. But I am afraid that memalloc_noio_save/ >> memalloc_noio_restore can not solve my problem. __GFP_IO is cleared >> if PF_MEMALLOC_NOIO is set and can avoid doing IO in direct memory >> reclaim. > > Well, yes. It sets a process flag that is used to avoid re-entrancy > issues in direct reclaim. Direct reclaim is more than just the > superblock shrinker - there are lots of other shrinkers, page > reclaim, etc and I bet there are other paths that can trigger the > deadlock you are seeing. We need to protect against all those > cases, not just the one shrinker you see a problem with. i.e. we > need to clear __GPF_FS from *all* reclaim, not just the superblock > shrinker. > > Also, PF_FSTRANS is used internally by filesystems, not the > generic code. If we start spreading it through generic code like > this, we start breaking filesystems that rely on it having a > specific, filesystem internal meaning. So it's a NACK on that basis > as well. > >> However, __GFP_FS is still set that can not avoid pruning >> dcache and icache in memory allocation, resulting in the deadlock I >> described. > > You have a deadlock in direct reclaim, and we already have a > template for setting a process flag that is used to indirectly > control direct reclaim behaviour. If the current process flag > doesn't provide precisely the coverage, then use that implementation > as the template to do exactly what is needed for your case. > > Cheers, > > Dave. > Thanks very much for your advise. I will send another patch later. Thanks, Xuejiufei -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
