Re: [PATCH] fix flags length in net 9p

From: Steven Rostedt
Date: Thu May 01 2008 - 17:50:49 EST




On Fri, 2 May 2008, Alexey Dobriyan wrote:

> On Thu, May 01, 2008 at 02:19:19PM -0700, Andrew Morton wrote:
> > On Thu, 1 May 2008 17:08:05 -0400 (EDT)
> > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> >
> > > Some files in the net/9p directory uses "int" for flags. This can
> > > cause hard to find bugs on some architectures. This patch converts the
> > > flags to use "long" instead.
> >
> > gargh.
> >
> > > This bug was discovered by doing an allyesconfig make on the -rt kernel
> > > where checks are done to ensure all flags are of size sizeof(long).
> >
> > I was about to suggest that we do something like that...
> >
> > I wonder how messy it is. I long ago lost the ability to follow the
> > convolutions in include/linux/spinlock*.h :( gotta patch?
>
> Me, me, take me back!
>
>
> commit ee3ce191e8eaa4cc15c51a28b34143b36404c4f5
> Author: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Date: Sat Nov 25 11:09:36 2006 -0800
>
> [PATCH] Enforce "unsigned long flags;" when spinlocking
>
> Make it break or warn if you pass to spin_lock_irqsave() and friends
> something different from "unsigned long flags;". Suprisingly large amount
> of these was caught by recent commit
> c53421b18f205c5f97c604ae55c6a921f034b0f6 and others.
>
> Idea is largely from FRV typechecking. Suggestions from Andrew Morton.
> All stupid typos in first version fixed.
>
> Passes allmodconfig on i386, x86_64, alpha, arm as well as my usual config.
>
> Note #1: checking with sparse is still needed, because a driver can save
> and pass around flags or something. So far patch is very intrusive.
> Note #2: techically, we should break only if
> sizeof(flags) < sizeof(unsigned long),
> however, the more pain for getting suspicious code into kernel,
> the better.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>
>
> diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
> index 412e025..4fe740b 100644
> --- a/include/linux/irqflags.h
> +++ b/include/linux/irqflags.h
> @@ -11,6 +11,12 @@
> #ifndef _LINUX_TRACE_IRQFLAGS_H
> #define _LINUX_TRACE_IRQFLAGS_H
>
> +#define BUILD_CHECK_IRQ_FLAGS(flags) \
> + do { \
> + BUILD_BUG_ON(sizeof(flags) != sizeof(unsigned long)); \
> + typecheck(unsigned long, flags); \
> + } while (0)
> +
> #ifdef CONFIG_TRACE_IRQFLAGS
> extern void trace_hardirqs_on(void);
> extern void trace_hardirqs_off(void);
> @@ -50,10 +56,15 @@
> #define local_irq_disable() \
> do { raw_local_irq_disable(); trace_hardirqs_off(); } while (0)
> #define local_irq_save(flags) \
> - do { raw_local_irq_save(flags); trace_hardirqs_off(); } while (0)
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + raw_local_irq_save(flags); \
> + trace_hardirqs_off(); \
> + } while (0)
>
> #define local_irq_restore(flags) \
> do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> if (raw_irqs_disabled_flags(flags)) { \
> raw_local_irq_restore(flags); \
> trace_hardirqs_off(); \
> @@ -69,8 +80,16 @@
> */
> # define raw_local_irq_disable() local_irq_disable()
> # define raw_local_irq_enable() local_irq_enable()
> -# define raw_local_irq_save(flags) local_irq_save(flags)
> -# define raw_local_irq_restore(flags) local_irq_restore(flags)
> +# define raw_local_irq_save(flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + local_irq_save(flags); \
> + } while (0)
> +# define raw_local_irq_restore(flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + local_irq_restore(flags); \
> + } while (0)
> #endif /* CONFIG_TRACE_IRQFLAGS_SUPPORT */
>
> #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT
> @@ -80,7 +99,11 @@
> raw_safe_halt(); \
> } while (0)
>
> -#define local_save_flags(flags) raw_local_save_flags(flags)
> +#define local_save_flags(flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + raw_local_save_flags(flags); \
> + } while (0)
>
> #define irqs_disabled() \
> ({ \
> @@ -90,7 +113,11 @@
> raw_irqs_disabled_flags(flags); \
> })
>
> -#define irqs_disabled_flags(flags) raw_irqs_disabled_flags(flags)
> +#define irqs_disabled_flags(flags) \
> +({ \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + raw_irqs_disabled_flags(flags); \
> +})
> #endif /* CONFIG_X86 */
>
> #endif
> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
> index b800d2d..54ad370 100644
> --- a/include/linux/spinlock.h
> +++ b/include/linux/spinlock.h
> @@ -52,6 +52,7 @@
> #include <linux/thread_info.h>
> #include <linux/kernel.h>
> #include <linux/stringify.h>
> +#include <linux/irqflags.h>
>
> #include <asm/system.h>
>
> @@ -183,13 +184,37 @@ do { \
> #define read_lock(lock) _read_lock(lock)
>
> #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
> -#define spin_lock_irqsave(lock, flags) flags = _spin_lock_irqsave(lock)
> -#define read_lock_irqsave(lock, flags) flags = _read_lock_irqsave(lock)
> -#define write_lock_irqsave(lock, flags) flags = _write_lock_irqsave(lock)
> +#define spin_lock_irqsave(lock, flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + flags = _spin_lock_irqsave(lock); \
> + } while (0)
> +#define read_lock_irqsave(lock, flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + flags = _read_lock_irqsave(lock); \
> + } while (0)
> +#define write_lock_irqsave(lock, flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + flags = _write_lock_irqsave(lock); \
> + } while (0)
> #else
> -#define spin_lock_irqsave(lock, flags) _spin_lock_irqsave(lock, flags)
> -#define read_lock_irqsave(lock, flags) _read_lock_irqsave(lock, flags)
> -#define write_lock_irqsave(lock, flags) _write_lock_irqsave(lock, flags)
> +#define spin_lock_irqsave(lock, flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + _spin_lock_irqsave(lock, flags); \
> + } while (0)
> +#define read_lock_irqsave(lock, flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + _read_lock_irqsave(lock, flags); \
> + } while (0)
> +#define write_lock_irqsave(lock, flags) \
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + _write_lock_irqsave(lock, flags); \
> + } while (0)
> #endif
>
> #define spin_lock_irq(lock) _spin_lock_irq(lock)
> @@ -225,15 +250,24 @@ do { \
> #endif
>
> #define spin_unlock_irqrestore(lock, flags) \
> - _spin_unlock_irqrestore(lock, flags)
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + _spin_unlock_irqrestore(lock, flags); \
> + } while (0)
> #define spin_unlock_bh(lock) _spin_unlock_bh(lock)
>
> #define read_unlock_irqrestore(lock, flags) \
> - _read_unlock_irqrestore(lock, flags)
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + _read_unlock_irqrestore(lock, flags); \
> + } while (0)
> #define read_unlock_bh(lock) _read_unlock_bh(lock)
>
> #define write_unlock_irqrestore(lock, flags) \
> - _write_unlock_irqrestore(lock, flags)
> + do { \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> + _write_unlock_irqrestore(lock, flags); \
> + } while (0)
> #define write_unlock_bh(lock) _write_unlock_bh(lock)
>
> #define spin_trylock_bh(lock) __cond_lock(lock, _spin_trylock_bh(lock))
> @@ -247,6 +281,7 @@ do { \
>
> #define spin_trylock_irqsave(lock, flags) \
> ({ \
> + BUILD_CHECK_IRQ_FLAGS(flags); \
> local_irq_save(flags); \
> spin_trylock(lock) ? \
> 1 : ({ local_irq_restore(flags); 0; }); \
>
>
>
> Seriously, if people can suggest _good_ *** for the following idiom
>
> flags = spin_lock_irq***(&lock);
> ...
> spin_unlock_irqrestore(&lock, flags);
>
> I can do tree-wide conversion with irq_flags_t and new locking
> primitive.

I don't think we need to have a new primitive.

>
> If people can't, I can do just irq_flags_t conversion and enforce build
> breakage if one use something other than irq_flags_t .

We can simply have all users of flags use the new irqflags_t type, and
just do a one time big patch (grant you, that would break all pending
patches before that). But we can also write up a script that can convert
patches as well.

-- Steve

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