[Crash-utility] [PATCH] Fix for "files -[cp]" options on Linux 4.17

[Dave Anderson]

----- Original Message -----
> Since the kernel commit b93b016313b3ba8003c3b8bb71f569af91f19fc7
> ("page cache: use xa_lock") renamed the address_space ->page_tree
> to ->i_pages, without this patch, the "files -[cp]" options don't
> work on Linux 4.17 and later kernels.
> (In this case, is it OK not to add a new member to offset_table?)

Sure, that's fine.

> 
> Also, it looks like the address_space's member that the "files -c"
> option really requires is ->nrpages, not ->page_tree.

Looks right to me.  

I also noticed this is an attempt is made to dump the page cache contents
when nrpages count is 0:

  crash> files -p ffff8803c8d67038
       INODE        NRPAGES
  ffff8803c8d67038        0

  files: do_radix_tree: callback operation failed: entry: 0  item: 0
  crash>

So I added this:

--- filesys.c	2018-08-09 10:51:41.657042511 -0400
+++ filesys.c	2018-09-04 11:46:02.186072870 -0400
@@ -2207,6 +2207,11 @@ dump_inode_page_cache_info(ulong inode)
 		RJUST|LONG_DEC,
 		MKSTR(nrpages)));
 
+	FREEBUF(inode_buf);
+
+	if (!nrpages)
+		return;
+
 	root_rnode = i_mapping + OFFSET(address_space_page_tree);
 	rtp.index = 0;
 	rtp.value = (void *)&dump_inode_page;
@@ -2217,7 +2222,6 @@ dump_inode_page_cache_info(ulong inode)
 		error(INFO, "page_tree count: %ld  nrpages: %ld\n",
 			count, nrpages);
 
-	FREEBUF(inode_buf);
 	return;
 }

But then again, I note that "files -p" fails quite frequently due to 
some kind of mis-use of the contents of the radix tree.  The 2 options 
were introduced together in crash-7.1.2, but I've never really used them.

Anyway, the patch is queued for crash-7.2.4:

  https://github.com/crash-utility/crash/commit/2f57a96ce27d8b121c2822de2a66c71b83bdad21

Thanks,
  Dave







 
> Signed-off-by: Kazuhito Hagio <k-hagio at ab.jp.nec.com>
> ---
>  filesys.c | 2 +-
>  memory.c  | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/filesys.c b/filesys.c
> index 47f5a24..527b3f6 100644
> --- a/filesys.c
> +++ b/filesys.c
> @@ -2275,7 +2275,7 @@ cmd_files(void)
>  			return;
>  
>  		case 'c':
> -			if (VALID_MEMBER(address_space_page_tree) &&
> +			if (VALID_MEMBER(address_space_nrpages) &&
>  			    VALID_MEMBER(inode_i_mapping))
>  				open_flags |= PRINT_NRPAGES;
>  			else
> diff --git a/memory.c b/memory.c
> index 24fce5e..ea25047 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -487,6 +487,8 @@ vm_init(void)
>  	MEMBER_OFFSET_INIT(block_device_bd_disk, "block_device", "bd_disk");
>  	MEMBER_OFFSET_INIT(inode_i_mapping, "inode", "i_mapping");
>  	MEMBER_OFFSET_INIT(address_space_page_tree, "address_space", "page_tree");
> +	if (INVALID_MEMBER(address_space_page_tree))
> +		MEMBER_OFFSET_INIT(address_space_page_tree, "address_space", "i_pages");
>  	MEMBER_OFFSET_INIT(address_space_nrpages, "address_space", "nrpages");
>  	if (INVALID_MEMBER(address_space_nrpages))
>  		MEMBER_OFFSET_INIT(address_space_nrpages, "address_space", "__nrpages");
> --
> 1.8.3.1
> 
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