On Fri, 2014-11-14 at 15:50 +0300, Andrey Ryabinin wrote:
> On architectures that have support for efficient unaligned access
> struct printk_log has 4-byte alignment.
> Specify alignment attribute in type declaration.
>
> The whole point of this patch is to fix deadlock which happening
> when UBSan detects unaligned access in printk() thus UBSan recursively
> calls printk() with logbuf_lock held by top printk() call.
[]
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
[]
> @@ -223,7 +223,11 @@ struct printk_log {
> u8 facility; /* syslog facility */
> u8 flags:5; /* internal record flags */
> u8 level:3; /* syslog level */
> -};
> +}
> +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> +__packed __aligned(4)
> +#endif
Why is adding __packed useful or __aligned(4) useful?
The struct is naturally aligned on u64 and should be
the size of 2 u64s.
struct printk_log {
u64 ts_nsec; /* timestamp in nanoseconds */
u16 len; /* length of entire record */
u16 text_len; /* length of text buffer */
u16 dict_len; /* length of dictionary buffer */
u8 facility; /* syslog facility */
u8 flags:5; /* internal record flags */
u8 level:3; /* syslog level */
};
Is there any case when it's not sizeof(u64) * 2?
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