linux-ext4 - Re: [PATCH v6 00/19] Change readahead API

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Message-ID: <20200219034832.GL24185@bombadil.infradead.org>
Date:   Tue, 18 Feb 2020 19:48:32 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        ocfs2-devel@....oracle.com, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v6 00/19] Change readahead API

On Wed, Feb 19, 2020 at 02:45:25PM +1100, Dave Chinner wrote:
> 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:
> > > 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.
> 
> 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....

Eric found it ... still not sure why I don't see it.