linux-kernel - Re: [PATCH] f2fs: fix unaligned field offset in 32-bits platform

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Date:   Thu, 9 Mar 2023 15:25:49 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Zhiguo Niu <zhiguo.niu@...soc.com>
Subject: Re: [PATCH] f2fs: fix unaligned field offset in 32-bits platform

On 03/07, Chao Yu wrote:
> F2FS-fs (dm-x): inconsistent rbtree, cur(3470333575168) next(3320009719808)
> ------------[ cut here ]------------
> kernel BUG at fs/f2fs/gc.c:602!
> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
> PC is at get_victim_by_default+0x13c0/0x1498
> LR is at f2fs_check_rb_tree_consistence+0xc4/0xd4
> ....
> [<c04d98b0>] (get_victim_by_default) from [<c04d4f44>] (f2fs_gc+0x220/0x6cc)
> [<c04d4f44>] (f2fs_gc) from [<c04d4780>] (gc_thread_func+0x2ac/0x708)
> [<c04d4780>] (gc_thread_func) from [<c015c774>] (kthread+0x1a8/0x1b4)
> [<c015c774>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20)
> 
> The reason is there is __packed attribute in struct rb_entry, but there
> is no __packed attribute in struct victim_entry, so wrong offset of key
> field will be parsed in struct rb_entry in f2fs_check_rb_tree_consistence,
> it describes memory layouts of struct rb_entry and struct victim_entry in
> 32-bits platform as below:
> 
> struct rb_entry {
>    [0] struct rb_node rb_node;
>        union {
>            struct {...};
>   [12]     unsigned long long key;
>        } __packed;
> }
> size of struct rb_entry: 20
> 
> struct victim_entry {
>    [0] struct rb_node rb_node;
>        union {
>            struct {...};
>   [16]     struct victim_info vi;

Why 16?
Don't we get the key from "unsigned long long mtime" starting at [12]?

	struct rb_node rb_node;		/* rb node located in rb-tree */
	union {
		struct {
			unsigned long long mtime;	/* mtime of section */
			unsigned int segno;		/* segment No. */
		};
		struct victim_info vi;	/* victim info */
	}; 

>        };
>   [32] struct list_head list;
> }
> size of struct victim_entry: 40
> 
> This patch tries to add __packed attribute in below structure:
> - discard_info, discard_cmd
> - extent_info, extent_node
> - victim_info, victim_entry
> in order to fix this unaligned field offset issue in 32-bits platform.
> 
> Fixes: 004b68621897 ("f2fs: use rb-tree to track pending discard commands")
> Fixes: 13054c548a1c ("f2fs: introduce infra macro and data structure of rb-tree extent cache")
> Fixes: 093749e296e2 ("f2fs: support age threshold based garbage collection")
> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
> Signed-off-by: Chao Yu <chao@...nel.org>
> ---
>  fs/f2fs/f2fs.h | 6 +++---
>  fs/f2fs/gc.h   | 4 ++--
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index b0ab2062038a..17fa7572ceed 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -349,7 +349,7 @@ struct discard_info {
>  	block_t lstart;			/* logical start address */
>  	block_t len;			/* length */
>  	block_t start;			/* actual start address in dev */
> -};
> +} __packed;
>  
>  struct discard_cmd {
>  	struct rb_node rb_node;		/* rb node located in rb-tree */
> @@ -361,7 +361,7 @@ struct discard_cmd {
>  		};
>  		struct discard_info di;	/* discard info */
>  
> -	};
> +	} __packed;
>  	struct list_head list;		/* command list */
>  	struct completion wait;		/* compleation */
>  	struct block_device *bdev;	/* bdev */
> @@ -660,7 +660,7 @@ struct extent_info {
>  			unsigned long long last_blocks;
>  		};
>  	};
> -};
> +} __packed;
>  
>  struct extent_node {
>  	struct rb_node rb_node;		/* rb node located in rb-tree */
> diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
> index 15bd1d680f67..304937d9a084 100644
> --- a/fs/f2fs/gc.h
> +++ b/fs/f2fs/gc.h
> @@ -58,7 +58,7 @@ struct gc_inode_list {
>  struct victim_info {
>  	unsigned long long mtime;	/* mtime of section */
>  	unsigned int segno;		/* section No. */
> -};
> +} __packed;
>  
>  struct victim_entry {
>  	struct rb_node rb_node;		/* rb node located in rb-tree */
> @@ -68,7 +68,7 @@ struct victim_entry {
>  			unsigned int segno;		/* segment No. */
>  		};
>  		struct victim_info vi;	/* victim info */
> -	};
> +	} __packed;
>  	struct list_head list;
>  };
>  
> -- 
> 2.36.1