Re: [PATCH v6 00/19] Change readahead API

Dave Chinner
2020-02-18T21:27:03Z

On Tue, Feb 18, 2020 at 05:42:30AM -0800, Matthew Wilcox wrote:
> On Tue, Feb 18, 2020 at 03:56:33PM +1100, Dave Chinner wrote:
> > Latest version in your git tree:
> >
> > $ ▶ glo -n 5 willy/readahead
> > 4be497096c04 mm: Use memalloc_nofs_save in readahead path
> > ff63497fcb98 iomap: Convert from readpages to readahead
> > 26aee60e89b5 iomap: Restructure iomap_readpages_actor
> > 8115bcca7312 fuse: Convert from readpages to readahead
> > 3db3d10d9ea1 f2fs: Convert from readpages to readahead
> > $
> >
> > merged into a 5.6-rc2 tree fails at boot on my test vm:
> >
> > [ 2.423116] ------------[ cut here ]------------
> > [ 2.424957] list_add double add: new=ffffea000efff4c8, prev=ffff8883bfffee60, next=ffffea000efff4c8.
> > [ 2.428259] WARNING: CPU: 4 PID: 1 at lib/list_debug.c:29 __list_add_valid+0x67/0x70
> > [ 2.457484] Call Trace:
> > [ 2.458171] __pagevec_lru_add_fn+0x15f/0x2c0
> > [ 2.459376] pagevec_lru_move_fn+0x87/0xd0
> > [ 2.460500] ? pagevec_move_tail_fn+0x2d0/0x2d0
> > [ 2.461712] lru_add_drain_cpu+0x8d/0x160
> > [ 2.462787] lru_add_drain+0x18/0x20
>
> Are you sure that was 4be497096c04 ? I ask because there was a

Yes, because it's the only version I've actually merged into my
working tree, compiled and tried to run. :P

> version pushed to that git tree that did contain a list double-add
> (due to a mismerge when shuffling patches). I noticed it and fixed
> it, and 4be497096c04 doesn't have that problem. I also test with
> CONFIG_DEBUG_LIST turned on, but this problem you hit is going to be
> probabilistic because it'll depend on the timing between whatever other
> list is being used and the page actually being added to the LRU.

I'll see if I can reproduce it.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com