Re: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ?

[Matt Mackall <mpm@selenic.com>]

On Fri, Dec 14, 2007 at 06:02:06PM -0800, Andrew Morton wrote:
> On Sat, 15 Dec 2007 01:09:41 +0000 Mel Gorman <mel@csn.ul.ie> wrote:
> 
> > On (13/12/07 14:29), Andrew Morton didst pronounce:
> > > > The simple way seems to be to malloc a large area, touch every page and
> > > > then look at the physical pages assigned ... they now mostly seem to be
> > > > descending in physical address.
> > > > 
> > > 
> > > OIC.  -mm's /proc/pid/pagemap can be used to get the pfn's...
> > > 
> > 
> > I tried using pagemap to verify the patch but it triggered BUG_ON
> > checks. Perhaps I am using the interface wrong but I would still not
> > expect it to break in this fashion. I tried 2.6.24-rc4-mm1, 2.6.24-rc5-mm1,
> > 2.6.24-rc5 with just the maps4 patches applied and 2.6.23 with maps4 patches
> > applied. Each time I get errors like this;
> > 
> > [   90.108315] BUG: sleeping function called from invalid context at include/asm/uaccess_32.h:457
> > [   90.211227] in_atomic():1, irqs_disabled():0
> > [   90.262251] no locks held by showcontiguous/2814.
> > [   90.318475] Pid: 2814, comm: showcontiguous Not tainted 2.6.24-rc5 #1
> > [   90.395344]  [<c010522a>] show_trace_log_lvl+0x1a/0x30
> > [   90.456948]  [<c0105bb2>] show_trace+0x12/0x20
> > [   90.510173]  [<c0105eee>] dump_stack+0x6e/0x80
> > [   90.563409]  [<c01205b3>] __might_sleep+0xc3/0xe0
> > [   90.619765]  [<c02264fd>] copy_to_user+0x3d/0x60
> > [   90.675153]  [<c01b3e9c>] add_to_pagemap+0x5c/0x80
> > [   90.732513]  [<c01b43e8>] pagemap_pte_range+0x68/0xb0
> > [   90.793010]  [<c0175ed2>] walk_page_range+0x112/0x210
> > [   90.853482]  [<c01b47c6>] pagemap_read+0x176/0x220
> > [   90.910863]  [<c0182dc4>] vfs_read+0x94/0x150
> > [   90.963058]  [<c01832fd>] sys_read+0x3d/0x70
> > [   91.014219]  [<c0104262>] syscall_call+0x7/0xb
> > 
> > ...
> >
> > Just using cp to read the file is enough to cause problems but I included
> > a very basic program below that produces the BUG_ON checks. Is this a known
> > issue or am I using the interface incorrectly?
> 
> I'd say you're using it correctly but you've found a hitherto unknown bug. 
> On i386 highmem machines with CONFIG_HIGHPTE (at least) pte_offset_map()
> takes kmap_atomic(), so pagemap_pte_range() can't do copy_to_user() as it
> presently does.

Damn, I coulda sworn I fixed that.

-- 
Mathematics is the supreme nostalgia of our time.