linux-kernel - Re: [BUG] Lockless patches cause hardlock under heavy IO

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Date:	Tue, 24 Jun 2008 09:12:51 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ryan Hope <rmh3093@...il.com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-mm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] Lockless patches cause hardlock under heavy IO

On Tue, Jun 24, 2008 at 11:57:05AM -0400, Ryan Hope wrote:
> I can give you a list of patches that should correspond to the thread
> name (for the most part):
> 
> fix-double-unlock_page-in-2626-rc5-mm3-kernel-bug-at-mm-filemapc-575.patch
> 
> fix_munlock-page-table-walk.patch
> 
> migration_entry_wait-fix.patch
> 
> PATCH collect lru meminfo statistics from correct offset
> 
> Mlocked field of /proc/meminfo display silly number.
> because trivial mistake exist in meminfo_read_proc().
> 
> You can also look in our git repo to see the code that changed with
> these patches if you cant track them down in LKML:
> http://zen-sources.org/cgi-bin/gitweb.cgi?p=kernel-mm.git;a=shortlog;h=refs/heads/lkml

Thank you!  And is this using Classic RCU or Preemptable RCU?

							Thanx, Paul

> On Tue, Jun 24, 2008 at 11:32 AM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > On Tue, Jun 24, 2008 at 11:12:03AM -0400, Ryan Hope wrote:
> >> Well i tried to run pure -mm this weekend, it locked as soon as I got
> >> into gnome so I applied a couple of the bug fixes from lkml and -mm
> >> seems to be running stable now. I cant seem to get it to hard lock
> >> now, at least not doing the simple stuff that was causing it to hard
> >> lock on my other patchset, either the lockless patches expose some bug
> >> that in -rc6 or lockless requires some other patches further up in the
> >> -mm series file.
> >
> > Cool!!!  Any guess as to which of the bug fixes did the trick?
> > Failing that, a list of the bug fixes that you applied?
> >
> >                                                        Thanx, Paul
> >
> >> On Mon, Jun 23, 2008 at 8:13 PM, Nick Piggin <nickpiggin@...oo.com.au> wrote:
> >> > On Monday 23 June 2008 23:05, Paul E. McKenney wrote:
> >> >> On Mon, Jun 23, 2008 at 09:54:52PM +1000, Nick Piggin wrote:
> >> >> > On Monday 23 June 2008 13:51, Ryan Hope wrote:
> >> >> > > well i get the hardlock on -mm with out using reiser4, i am pretty
> >> >> > > sure is swap related
> >> >> >
> >> >> > The guys seeing hangs don't use PREEMPT_RCU, do they?
> >> >> >
> >> >> > In my swapping tests, I found -mm3 to be stable with classic RCU, but
> >> >> > on a hunch, I tried PREEMPT_RCU and it crashed a couple of times rather
> >> >> > quickly. First crash was in find_get_pages so I suspected lockless
> >> >> > pagecache doing something subtly wrong with the RCU API, but I just got
> >> >> > another crash in __d_lookup:
> >> >>
> >> >> Could you please send me a repeat-by?  (At least Alexey is no longer
> >> >> alone!)
> >> >
> >> > OK, I had DEBUG_PAGEALLOC in the .config, which I think is probably
> >> > important to reproduce it (but the fact that I'm reproducing oopses
> >> > with << PAGE_SIZE objects like dentries and radix tree nodes indicates
> >> > that there is even more free-before-grace activity going undetected --
> >> > if you construct a test case using full pages, it might become even
> >> > easier to detect with DEBUG_PAGEALLOC).
> >> >
> >> > 2 socket, 8 core x86 system.
> >> >
> >> > I mounted two tmpfs filesystems, one contains a single large file
> >> > which is formatted as 1K block size ext3 and mounted loopback, the
> >> > other is used directly. Linux kernel source is unpacked on each mount
> >> > and concurrent make -j128 on each. This pushes it pretty hard into
> >> > swap. Classic RCU survived another 5 hours of this last night.
> >> >
> >> > But that's a fairly convoluted test for an RCU problem. I expect it
> >> > should be easier to trigger with something more targetted...
> >> >
> >
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