Hi Guys, "> It's limited to xfs, no failure on ext4 to date", this is incorrect. I have been able to reproduce this issue with ext4. In order to do that, I need to run the full test (on both pmems in the system) and not the half test (only 1 pmem) that I use for inducing the hang under XFS. The test also runs considerably longer before failing with ext4 than XFS. Thx bob -----Original Message----- From: Dave Chinner [mailto:david@xxxxxxxxxxxxx] Sent: Monday, March 11, 2019 9:38 PM To: Williams, Dan J <dan.j.williams@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>; Linux MM <linux-mm@xxxxxxxxx>; linux-nvdimm <linux-nvdimm@xxxxxxxxxxxx>; linux-fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>; Barror, Robert <robert.barror@xxxxxxxxx> Subject: Re: Hang / zombie process from Xarray page-fault conversion (bisected) On Mon, Mar 11, 2019 at 08:35:05PM -0700, Dan Williams wrote: > On Mon, Mar 11, 2019 at 8:10 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Thu, Mar 07, 2019 at 10:16:17PM -0800, Dan Williams wrote: > > > Hi Willy, > > > > > > We're seeing a case where RocksDB hangs and becomes defunct when > > > trying to kill the process. v4.19 succeeds and v4.20 fails. Robert > > > was able to bisect this to commit b15cd800682f "dax: Convert page > > > fault handlers to XArray". > > > > > > I see some direct usage of xa_index and wonder if there are some > > > more pmd fixups to do? > > > > > > Other thoughts? > > > > I don't see why killing a process would have much to do with PMD > > misalignment. The symptoms (hanging on a signal) smell much more > > like leaving a locked entry in the tree. Is this easy to reproduce? > > Can you get /proc/$pid/stack for a hung task? > > It's fairly easy to reproduce, I'll see if I can package up all the > dependencies into something that fails in a VM. > > It's limited to xfs, no failure on ext4 to date. > > The hung process appears to be: > > kworker/53:1-xfs-sync/pmem0 That's completely internal to XFS. Every 30s the work is triggered and it either does a log flush (if the fs is active) or it syncs the superblock to clean the log and idle the filesystem. It has nothing to do with user processes, and I don't see why killing a process has any effect on what it does... > ...and then the rest of the database processes grind to a halt from there. > > Robert was kind enough to capture /proc/$pid/stack, but nothing interesting: > > [<0>] worker_thread+0xb2/0x380 > [<0>] kthread+0x112/0x130 > [<0>] ret_from_fork+0x1f/0x40 > [<0>] 0xffffffffffffffff Much more useful would be: # echo w > /proc/sysrq-trigger And post the entire output of dmesg. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
