On Tue, May 26 2009, Damien Wyart wrote: > > > I have been playing with v7 since your sending and after a while > > > (short on laptop, longer on desktop, a few hours), writeback doesn't > > > seem to work anymore. Manual call to sync hangs (process in D state) > > > and Dirty value in meminfo gets growing. As previous versions had > > > been heavily tested, I guess there is some regression in v7. > > > Not good, the prime suspect is the sync notification stuff. I'll take > > a look and get that fixed. You didn't happen to catch any sysrq-t back > > traces or anything like that? Would be interesting to see where > > bdi-default and the bdi-* threads are stuck. > > No, as I was doing many things at the same time and not exclusively > debugging, I just rebooted hard and went back to an upatched kernel when > the problems occured. But I noticed only bdi-default was alive, the > other bdi-* threads had disappeared and the sync commands I had tried > were all in D state. Also I tried to reinstall a kernel .deb (these > systems are Debian) and this got stuck guring installation, when probing > grub config (do not know if there is some sync syscall inthere). > > Can try to go further tomorrow but will not have a lot of time... OK, I spotted the problem. If we fallback to the on-stack allocation in bdi_writeback_all(), then we do the wait for the work completion with the bdi_lock mutex held. This can deadlock with bdi_forker_task(), so if we require that to be invoked to make progress (happens if a thread needs to be restarted), then we have a deadlock on that mutex. I'll cook up a fix for this, but probably not before the morning. -- Jens Axboe -- 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
