From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xue jiufei Date: Fri, 29 Aug 2014 15:22:11 +0800 Subject: [Ocfs2-devel] A deadlock when system do not has sufficient memory In-Reply-To: <53FFF2FB.20706@oracle.com> References: <53F41CAE.2040204@huawei.com> <53F6FFB7.1090305@huawei.com> <53FA9673.20205@oracle.com> <53FEE543.10407@huawei.com> <53FFF2FB.20706@oracle.com> Message-ID: <54002A23.6050708@huawei.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com On 2014/8/29 11:26, Junxiao Bi wrote: > On 08/28/2014 04:16 PM, Xue jiufei wrote: >> Hi Junxiao, >> On 2014/8/25 9:50, Junxiao Bi wrote: >>> Hi Jiufei, >>> >>> Maybe you can consider using PF_FSTRANS flag, set this flag before >>> allocating memory with GFP_KERNEL flag and unset after the allocation. >>> Checking this flag in ocfs2 when trying to free some pages during memory >>> direct reclaim. See an example from upstream commit >>> 5cf02d09b50b1ee1c2d536c9cf64af5a7d433f56 (nfs: skip commit in >>> releasepage if we're freeing memory for fs-related reasons) . >>> >>> Thanks, >>> Junxiao. >>> >> Thank you very much for your suggestion. But in our situation, >> o2net_wq is evicting inode during memory direct reclaim, which cannot >> return error or do nothing because vfs would destroy_inode after evict, >> but we haven't drop inode lock yet. > How about checking the flag in vfs like this? And you can set PF_FSTRANS > flag in o2net_wq context where GFP_NOFS flag can't be set. > > > commit 8d27fdec5ce234d2f02e4582d340d231396b92af > Author: Junxiao Bi > Date: Fri Aug 29 11:05:25 2014 +0800 > > super: stop shrinker for processes with PF_FSTRANS flag > > For some cluster fs, like ocfs2, it may be impossible to > set GFP_NOFS for some memory allocation, as the allocation > is in network common code, like sock_alloc() and in this > case, the shrinker will call back into the fs and cause > deadlock when available memory is not enough. > > Signed-off-by: Junxiao Bi > > diff --git a/fs/super.c b/fs/super.c > index b9a214d..c4a8dc1 100644 > --- a/fs/super.c > +++ b/fs/super.c > @@ -71,6 +71,9 @@ static unsigned long super_cache_scan(struct shrinker > *shrink, > if (!(sc->gfp_mask & __GFP_FS)) > return SHRINK_STOP; > > + if (current->flags & PF_FSTRANS) > + return SHRINK_STOP; > + > if (!grab_super_passive(sb)) > return SHRINK_STOP; > > > Thanks, > Junxiao. > Yes, this patch can resolve our problem. Thanks a lot. Have you send this patch to fs-devel list? >> >> Thanks >> Xuejiufei >> >>> On 08/22/2014 04:30 PM, Xue jiufei wrote: >>>> On 2014/8/20 11:57, Xue jiufei wrote: >>>>> Hi all, >>>>> We found there may exist a deadlock when system has not sufficient >>>>> memory. Here's the situation: >>>>> N1 N2 >>>>> send message to N1 >>>>> o2net_wq(kworker) >>>>> receiving message and call corresponding >>>>> handler to handle this message. It may >>>>> need to alloc some memory(use GFP_NOFS or GFP_KERNEL). >>>>> but there's no sufficient memory, lower then >>>>> min watermark. So it wakeup kswapd to reclaim memory >>>>> and itself may also call >>>>> __alloc_pages_direct_reclaim(), trying to >>>>> free some pages. >>>>> >>>>> It tries to free ocfs2 inode >>>>> cache and calls ocfs2_drop_lock()->dlmunlock() >>>>> to drop inode lock, sending unlock message to master, >>>>> say N2. When reply comes, queue sc_rx_work and >>>>> wait o2net_wq to handle this work. however >>>>> o2net_wq is still handling last message, so can not >>>>> process the reply message. It will wait >>>>> o2net_nsw_completed() in o2net_send_message_vec() >>>>> forever. >>>>> Kswapd thread enconter the same situation. >>>>> >>>>> >>>>> So is there any advice to solve this deadlock? >>>>> And what is the probability that kmalloc return ENOMEM when use GFP_ATOMIC flag? >>>>> >>>>> Thanks. >>>>> >>>> To avoid this deadlock, we want to alloc memory with flag GFP_ATOMIC >>>> in all handlers and return ENOMEM to peer when failed. The peer will >>>> try to resend the message again, o2net_wq can handle other messages. >>>> However, it can not solve all problems. For example, if o2net_wq is >>>> processing sc_connect_work which would call sock_alloc_inode() to alloc >>>> socket_alloc with GFP_KERNEL flag when memory is insufficient and enter >>>> reclaim progress, it also trigger the deadlock. We can not change this >>>> alloc flag. >>>> We have no idea about it. Is there any better ideas. >>>> Thanks very much. >>>> xuejiufei >>>>> _______________________________________________ >>>>> Ocfs2-devel mailing list >>>>> Ocfs2-devel at oss.oracle.com >>>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel >>>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Ocfs2-devel mailing list >>>> Ocfs2-devel at oss.oracle.com >>>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel >>>> >>> >>> . >>> >> >> > > . >