Hello, again. Adding Shaohua Li as he fixed a similar issue in 4a0b75c7d0 "block, cfq: fix empty queue crash caused by request merge". The original thread can be read from http://thread.gmane.org/gmane.linux.kernel.next/20064/focus=20159 On Tue, Jan 03, 2012 at 09:35:00AM -0800, Tejun Heo wrote: > Happy new year, guys. > > On Wed, Dec 28, 2011 at 01:19:18PM -0800, Tejun Heo wrote: > > > On Wed, Dec 28, 2011 at 9:50 AM, Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > > > "It's the tmpfs swapping test that I've been running, with variations, > > > > for years. System booted with mem=700M and 1.5G swap, two repetitious > > > > make -j20 kernel builds (of a 2.6.24 kernel: I stuck with that because > > > > the balance of built to unbuilt source grows smaller with later kernels), > > > > one directly in a tmpfs, the other in a 1k-block ext2 (that I drive with > > > > ext4's CONFIG_EXT4_USE_FOR_EXT23) on /dev/loop0 on a 450MB tmpfs file." > > > > > > > > I doubt much of that (quoted from an older mail to someone else about > > > > one of the many other bugs it's found) is relevant: maybe just plenty > > > > of file I/O and swapping. > > > > > > Plain -j4 build isn't triggering anything. I'll try to replicate the condition. > > > > It's not too reliable but I can reproduce it with -j 22 allmodconfig > > build inside qemu w/ 512M of memory. I'll try to find out what's > > going on. > > I misread the code, the problem is empty cfqq on the cfq prio tree. I > don't think this is caused by recent io_context changes. It looks > like somebody is forgetting to remove cfqq from the dispatch prio tree > after emptying a cfqq by removing a request from it. Jens, any ideas? That should have been service tree. I couldn't find more missing removals other than the one Shaohua's patch already fixed. Close cooperator selection in cfq_select_queue() seems suspicious tho. I can't see what prevents it from returning an empty coopeator cfqq. I'm trying to verify whether that's the case. Will update when I know more. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
