On Wed, Feb 19, 2020 at 08:26:52AM +1100, Dave Chinner wrote:

On Tue, Feb 18, 2020 at 05:42:30AM -0800, Matthew Wilcox wrote:

quoted

On Tue, Feb 18, 2020 at 03:56:33PM +1100, Dave Chinner wrote:

quoted

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

quoted

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.

Just updated to a current TOT Linus kernel and your latest branch,
and so far this is 100% reproducable.

Not sure how I'm going to debug it yet, because it's init that is
triggering it....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com