linux-kernel - Re: [peterz-queue:perf/core 18/22] kernel/events/core.c:6418:22: sparse: sparse: incorrect type in assignment (different address spaces)

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Message-ID: <YHgBTRciZNDUkfId@elver.google.com>
Date:   Thu, 15 Apr 2021 11:03:09 +0200
From:   Marco Elver <elver@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     kbuild-all@...ts.01.org, kernel test robot <lkp@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [peterz-queue:perf/core 18/22] kernel/events/core.c:6418:22:
 sparse: sparse: incorrect type in assignment (different address spaces)

On Thu, Apr 15, 2021 at 10:48AM +0200, Peter Zijlstra wrote:
> On Wed, Apr 14, 2021 at 04:33:22PM +0200, Marco Elver wrote:
> > On Wed, Apr 14, 2021 at 10:10PM +0800, kernel test robot wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/core
> > > head:   0da503cd07380952599b67ded6efe030d78ea42d
> > > commit: c7d4112e9f0e69edd649665836ce72008b95ab9f [18/22] perf: Add support for SIGTRAP on perf events
> > [...]
> > > If you fix the issue, kindly add following tag as appropriate
> > > Reported-by: kernel test robot <lkp@...el.com>
> > [...]
> > >   6416		info.si_errno = event->attr.type;
> > >   6417		info.si_perf = event->attr.sig_data;
> > > > 6418		info.si_addr = (void *)event->sig_addr;
> > >   6419		force_sig_info(&info);
> > 
> > I think it wants the below (feel free to squash into "perf: Add support
> > for SIGTRAP on perf events").
> > 
> > Thanks,
> > -- Marco
> > 
[...]
> 
> Now the silly robot complains about:
> 
> CC      kernel/events/core.o
> ../kernel/events/core.c: In function ‘perf_sigtrap’:
> ../kernel/events/core.c:6418:17: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> 6418 |  info.si_addr = (void __user *)event->sig_addr;
> 
> for all 32bit builds (because sig_addr is u64 and the pointer cast
> truncates bits).
> 
> This had me look a little harder at sig_addr and I figured it should be
> next to the pending fields for cache locality.
> 
> I've ended up with the below delta, does that work for you?

Thanks, that works for me. Do note that I explicitly chose u64 for
sig_addr/pending_addr because data->addr is u64. There might be a new
warning about the u64 to unsigned long assignment on 32 bit arches.

Perhaps it needs something ugly like this:

	info.si_addr = (void __user *)(unsigned long)event->pending_addr;

if pending_addr wants to be u64. Or just

	event->pending_addr = (unsigned long)data->addr;

if data->addr being u64 on 32 bit arches is simply overkill.

Thanks,
-- Marco

> ---
> 
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -735,6 +735,7 @@ struct perf_event {
>  	int				pending_wakeup;
>  	int				pending_kill;
>  	int				pending_disable;
> +	unsigned long			pending_addr;	/* SIGTRAP */
>  	struct irq_work			pending;
>  
>  	atomic_t			event_limit;
> @@ -778,9 +779,6 @@ struct perf_event {
>  	void *security;
>  #endif
>  	struct list_head		sb_list;
> -
> -	/* Address associated with event, which can be passed to siginfo_t. */
> -	u64				sig_addr;
>  #endif /* CONFIG_PERF_EVENTS */
>  };
>  
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6415,7 +6415,7 @@ static void perf_sigtrap(struct perf_eve
>  	info.si_code = TRAP_PERF;
>  	info.si_errno = event->attr.type;
>  	info.si_perf = event->attr.sig_data;
> -	info.si_addr = (void __user *)event->sig_addr;
> +	info.si_addr = (void __user *)event->pending_addr;
>  	force_sig_info(&info);
>  }
>  
> @@ -9137,7 +9137,7 @@ static int __perf_event_overflow(struct
>  	if (events && atomic_dec_and_test(&event->event_limit)) {
>  		ret = 1;
>  		event->pending_kill = POLL_HUP;
> -		event->sig_addr = data->addr;
> +		event->pending_addr = data->addr;
>  
>  		perf_event_disable_inatomic(event);
>  	}