linux-kernel - Re: [PATCH v9 07/61] xarray: Add the xa_lock to the radix_tree

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Date:   Thu, 12 Apr 2018 14:59:32 -0600
From:   Ross Zwisler <zwisler@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
        linux-nilfs@...r.kernel.org
Subject: Re: [PATCH v9 07/61] xarray: Add the xa_lock to the radix_tree_root

On Tue, Mar 13, 2018 at 7:25 AM, Matthew Wilcox <willy@...radead.org> wrote:
> From: Matthew Wilcox <mawilcox@...rosoft.com>
>
> This results in no change in structure size on 64-bit machines as it
> fits in the padding between the gfp_t and the void *.  32-bit machines
> will grow the structure from 8 to 12 bytes.  Almost all radix trees
> are protected with (at least) a spinlock, so as they are converted from
> radix trees to xarrays, the data structures will shrink again.
>
> Initialising the spinlock requires a name for the benefit of lockdep,
> so RADIX_TREE_INIT() now needs to know the name of the radix tree it's
> initialising, and so do IDR_INIT() and IDA_INIT().
>
> Also add the xa_lock() and xa_unlock() family of wrappers to make it
> easier to use the lock.  If we could rely on -fplan9-extensions in
> the compiler, we could avoid all of this syntactic sugar, but that
> wasn't added until gcc 4.6.
>
> Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
> Reviewed-by: Jeff Layton <jlayton@...nel.org>

This is causing build breakage in the radix tree test suite in the
current linux/master:

5d1365940a68 (linux/master) Merge
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

Here's the first breakage:

cc -I. -I../../include -g -O2 -Wall -D_LGPL_SOURCE -fsanitize=address
 -c -o idr.o idr.c
In file included from ./linux/radix-tree.h:6:0,
                 from ./linux/../../../../include/linux/idr.h:15,
                 from ./linux/idr.h:1,
                 from idr.c:4:
./linux/../../../../include/linux/idr.h: In function ‘idr_init_base’:
./linux/../../../../include/linux/radix-tree.h:129:2: warning:
implicit declaration of function ‘spin_lock_init’; did you mean
‘spinlock_t’? [-Wimplicit-function-declaration]
  spin_lock_init(&(root)->xa_lock);    \
  ^
./linux/../../../../include/linux/idr.h:126:2: note: in expansion of
macro ‘INIT_RADIX_TREE’
  INIT_RADIX_TREE(&idr->idr_rt, IDR_RT_MARKER);
  ^~~~~~~~~~~~~~~