Re: [PATCH v4] alpha: fix memory barriers so that they conform to the specification

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On Sat, May 23, 2020 at 06:26:54AM -0400, Mikulas Patocka wrote:
> The commits cd0e00c10672 and 92d7223a7423 broke boot on the Alpha Avanti
> platform. The patches move memory barriers after a write before the write.
> The result is that if there's iowrite followed by ioread, there is no
> barrier between them.
> 
> The Alpha architecture allows reordering of the accesses to the I/O space,
> and the missing barrier between write and read causes hang with serial
> port and real time clock.
> 
> This patch makes barriers confiorm to the specification.
> 
> 1. We add mb() before readX_relaxed and writeX_relaxed -
>    memory-barriers.txt claims that these functions must be ordered w.r.t.
>    each other. Alpha doesn't order them, so we need an explicit barrier.
> 2. We add mb() before reads from the I/O space - so that if there's a
>    write followed by a read, there should be a barrier between them.

You missed the second mb() in extern inline u16 readw(). Otherwise,

Acked-by: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>

> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Fixes: cd0e00c10672 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering")
> Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
> Cc: stable@xxxxxxxxxxxxxxx      # v4.17+
> 
> ---
>  arch/alpha/include/asm/io.h |   43 ++++++++++++++++++++++++++++---------------
>  arch/alpha/kernel/io.c      |   28 +++++++++++++++++++++-------
>  2 files changed, 49 insertions(+), 22 deletions(-)
> 
> Index: linux-stable/arch/alpha/include/asm/io.h
> ===================================================================
> --- linux-stable.orig/arch/alpha/include/asm/io.h	2020-05-23 10:01:22.000000000 +0200
> +++ linux-stable/arch/alpha/include/asm/io.h	2020-05-23 10:01:22.000000000 +0200
> @@ -310,14 +310,18 @@ static inline int __is_mmio(const volati
>  #if IO_CONCAT(__IO_PREFIX,trivial_io_bw)
>  extern inline unsigned int ioread8(void __iomem *addr)
>  {
> -	unsigned int ret = IO_CONCAT(__IO_PREFIX,ioread8)(addr);
> +	unsigned int ret;
> +	mb();
> +	ret = IO_CONCAT(__IO_PREFIX,ioread8)(addr);
>  	mb();
>  	return ret;
>  }
>  
>  extern inline unsigned int ioread16(void __iomem *addr)
>  {
> -	unsigned int ret = IO_CONCAT(__IO_PREFIX,ioread16)(addr);
> +	unsigned int ret;
> +	mb();
> +	ret = IO_CONCAT(__IO_PREFIX,ioread16)(addr);
>  	mb();
>  	return ret;
>  }
> @@ -358,7 +362,9 @@ extern inline void outw(u16 b, unsigned
>  #if IO_CONCAT(__IO_PREFIX,trivial_io_lq)
>  extern inline unsigned int ioread32(void __iomem *addr)
>  {
> -	unsigned int ret = IO_CONCAT(__IO_PREFIX,ioread32)(addr);
> +	unsigned int ret;
> +	mb();
> +	ret = IO_CONCAT(__IO_PREFIX,ioread32)(addr);
>  	mb();
>  	return ret;
>  }
> @@ -403,15 +409,18 @@ extern inline void __raw_writew(u16 b, v
>  
>  extern inline u8 readb(const volatile void __iomem *addr)
>  {
> -	u8 ret = __raw_readb(addr);
> +	u8 ret;
> +	mb();
> +	ret = __raw_readb(addr);
>  	mb();
>  	return ret;
>  }
>  
>  extern inline u16 readw(const volatile void __iomem *addr)
>  {
> -	u16 ret = __raw_readw(addr);
> +	u16 ret;
>  	mb();
> +	ret = __raw_readw(addr);
>  	return ret;
>  }
>  
> @@ -451,14 +460,18 @@ extern inline void __raw_writeq(u64 b, v
>  
>  extern inline u32 readl(const volatile void __iomem *addr)
>  {
> -	u32 ret = __raw_readl(addr);
> +	u32 ret;
> +	mb();
> +	ret = __raw_readl(addr);
>  	mb();
>  	return ret;
>  }
>  
>  extern inline u64 readq(const volatile void __iomem *addr)
>  {
> -	u64 ret = __raw_readq(addr);
> +	u64 ret;
> +	mb();
> +	ret = __raw_readq(addr);
>  	mb();
>  	return ret;
>  }
> @@ -487,14 +500,14 @@ extern inline void writeq(u64 b, volatil
>  #define outb_p		outb
>  #define outw_p		outw
>  #define outl_p		outl
> -#define readb_relaxed(addr)	__raw_readb(addr)
> -#define readw_relaxed(addr)	__raw_readw(addr)
> -#define readl_relaxed(addr)	__raw_readl(addr)
> -#define readq_relaxed(addr)	__raw_readq(addr)
> -#define writeb_relaxed(b, addr)	__raw_writeb(b, addr)
> -#define writew_relaxed(b, addr)	__raw_writew(b, addr)
> -#define writel_relaxed(b, addr)	__raw_writel(b, addr)
> -#define writeq_relaxed(b, addr)	__raw_writeq(b, addr)
> +#define readb_relaxed(addr)	(mb(), __raw_readb(addr))
> +#define readw_relaxed(addr)	(mb(), __raw_readw(addr))
> +#define readl_relaxed(addr)	(mb(), __raw_readl(addr))
> +#define readq_relaxed(addr)	(mb(), __raw_readq(addr))
> +#define writeb_relaxed(b, addr)	(mb(), __raw_writeb(b, addr))
> +#define writew_relaxed(b, addr)	(mb(), __raw_writew(b, addr))
> +#define writel_relaxed(b, addr)	(mb(), __raw_writel(b, addr))
> +#define writeq_relaxed(b, addr)	(mb(), __raw_writeq(b, addr))
>  
>  /*
>   * String version of IO memory access ops:
> Index: linux-stable/arch/alpha/kernel/io.c
> ===================================================================
> --- linux-stable.orig/arch/alpha/kernel/io.c	2020-05-23 10:01:22.000000000 +0200
> +++ linux-stable/arch/alpha/kernel/io.c	2020-05-23 10:01:22.000000000 +0200
> @@ -16,21 +16,27 @@
>  unsigned int
>  ioread8(void __iomem *addr)
>  {
> -	unsigned int ret = IO_CONCAT(__IO_PREFIX,ioread8)(addr);
> +	unsigned int ret;
> +	mb();
> +	ret = IO_CONCAT(__IO_PREFIX,ioread8)(addr);
>  	mb();
>  	return ret;
>  }
>  
>  unsigned int ioread16(void __iomem *addr)
>  {
> -	unsigned int ret = IO_CONCAT(__IO_PREFIX,ioread16)(addr);
> +	unsigned int ret;
> +	mb();
> +	ret = IO_CONCAT(__IO_PREFIX,ioread16)(addr);
>  	mb();
>  	return ret;
>  }
>  
>  unsigned int ioread32(void __iomem *addr)
>  {
> -	unsigned int ret = IO_CONCAT(__IO_PREFIX,ioread32)(addr);
> +	unsigned int ret;
> +	mb();
> +	ret = IO_CONCAT(__IO_PREFIX,ioread32)(addr);
>  	mb();
>  	return ret;
>  }
> @@ -148,28 +154,36 @@ EXPORT_SYMBOL(__raw_writeq);
>  
>  u8 readb(const volatile void __iomem *addr)
>  {
> -	u8 ret = __raw_readb(addr);
> +	u8 ret;
> +	mb();
> +	ret = __raw_readb(addr);
>  	mb();
>  	return ret;
>  }
>  
>  u16 readw(const volatile void __iomem *addr)
>  {
> -	u16 ret = __raw_readw(addr);
> +	u16 ret;
> +	mb();
> +	ret = __raw_readw(addr);
>  	mb();
>  	return ret;
>  }
>  
>  u32 readl(const volatile void __iomem *addr)
>  {
> -	u32 ret = __raw_readl(addr);
> +	u32 ret;
> +	mb();
> +	ret = __raw_readl(addr);
>  	mb();
>  	return ret;
>  }
>  
>  u64 readq(const volatile void __iomem *addr)
>  {
> -	u64 ret = __raw_readq(addr);
> +	u64 ret;
> +	mb();
> +	ret = __raw_readq(addr);
>  	mb();
>  	return ret;
>  }
> 



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