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On 4/11/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Wed, 2007-04-11 at 17:53 +0800, Zhao Forrest wrote: > > I got some new information: > > Before soft lockup message is out, we have: > > [root@nsgsh-dhcp-149 home]# cat /proc/slabinfo |grep buffer_head > > buffer_head 10927942 10942560 120 32 1 : tunables 32 > > 16 8 : slabdata 341955 341955 6 : globalstat 37602996 11589379 > > 1174373 6 0 1 6918 12166031 1013708 > > : cpustat 35254590 2350698 13610965 907286 > > > > Then after buffer_head is freed, we have: > > [root@nsgsh-dhcp-149 home]# cat /proc/slabinfo |grep buffer_head > > buffer_head 9542 36384 120 32 1 : tunables 32 16 > > 8 : slabdata 1137 1137 245 : globalstat 37602996 11589379 > > 1174373 6 0 1 6983 20507478 > > 1708818 : cpustat 35254625 2350704 16027174 1068367 > > > > Does this huge number of buffer_head cause the soft lockup? > > > __blkdev_put() takes the BKL and bd_mutex > invalidate_mapping_pages() tries to take the PageLock > > But no other looks seem held while free_buffer_head() is called > > All these locks are preemptible (CONFIG_PREEMPT_BKL?=y) and should not > hog the cpu like that, what preemption mode have you got selected? > (CONFIG_PREEMPT_VOLUNTARY?=y) These 2 kernel options are turned on by default in my kernel. Here's snip from .config # CONFIG_PREEMPT_NONE is not set CONFIG_PREEMPT_VOLUNTARY=y # CONFIG_PREEMPT is not set CONFIG_PREEMPT_BKL=y CONFIG_NUMA=y CONFIG_K8_NUMA=y > > Does this fix it? > > --- fs/buffer.c~ 2007-02-01 12:00:34.000000000 +0100 > +++ fs/buffer.c 2007-04-11 12:35:48.000000000 +0200 > @@ -3029,6 +3029,8 @@ out: > struct buffer_head *next = bh->b_this_page; > free_buffer_head(bh); > bh = next; > + > + cond_resched(); > } while (bh != buffers_to_free); > } > return ret; > So far I have run the test with patched kernel for 6 rounds, and didn't see the soft lockup. I think this patch should fix the problem. But what still confused me is that why do we need to invoke cond_resched() voluntarily since CONFIG_PREEMPT_VOLUNTARY and CONFIG_PREEMPT_BKL are both turned on? From my understanding these 2 options should make schedule happen even if CPU is under heavy load...... Thanks, Forrest - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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