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Date:   Wed, 13 Nov 2019 15:38:16 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, Ioannis Ilkos <ilkos@google.com>,
        minchan@google.com, primiano@google.com, fmayer@google.com,
        hjd@google.com, joaodias@google.com, joelaf@google.com,
        lalitm@google.com, rslawik@google.com, sspatil@google.com,
        timmurray@google.com, Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Changbin Du <changbin.du@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Joe Perches <joe@perches.com>,
        Kees Cook <keescook@chromium.org>, linux-mm@kvack.org,
        Michal Hocko <mhocko@suse.com>, Petr Mladek <pmladek@suse.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH] rss_stat: Add support to detect RSS updates of external
 mm
Message-ID: <20191113153816.14b95acd@gandalf.local.home>
In-Reply-To: <20191106024452.81923-1-joel@joelfernandes.org>
References: <20191106024452.81923-1-joel@joelfernandes.org>
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/me coming late to the party.


On Tue,  5 Nov 2019 21:44:51 -0500
"Joel Fernandes (Google)" <joel@joelfernandes.org> wrote:

> When a process updates the RSS of a different process, the rss_stat
> tracepoint appears in the context of the process doing the update. This
> can confuse userspace that the RSS of process doing the update is
> updated, while in reality a different process's RSS was updated.
> 
> This issue happens in reclaim paths such as with direct reclaim or
> background reclaim.
> 
> This patch adds more information to the tracepoint about whether the mm
> being updated belongs to the current process's context (curr field). We
> also include a hash of the mm pointer so that the process who the mm
> belongs to can be uniquely identified (mm_id field).
> 
> Also vsprintf.c is refactored a bit to allow reuse of hashing code.
> 
> Reported-by: Ioannis Ilkos <ilkos@google.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> ---
> Based on top of the commit in linux-next:
> 8342d836dc7c ("mm: emit tracepoint when RSS changes")
> 
> Google Bug: 140711541
> 
> Cc: minchan@google.com
> Cc: primiano@google.com
> Cc: ilkos@google.com
> Cc: fmayer@google.com
> Cc: hjd@google.com
> Cc: joaodias@google.com
> Cc: joelaf@google.com
> Cc: lalitm@google.com
> Cc: rslawik@google.com
> Cc: sspatil@google.com
> Cc: timmurray@google.com
> 
>  include/linux/mm.h          |  8 ++++----
>  include/linux/string.h      |  2 ++
>  include/trace/events/kmem.h | 32 +++++++++++++++++++++++++++++---
>  lib/vsprintf.c              | 36 +++++++++++++++++++++++++-----------
>  mm/memory.c                 |  4 ++--
>  5 files changed, 62 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 31d8cfb3d988..bfbe65ccffa3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1643,27 +1643,27 @@ static inline unsigned long get_mm_counter(struct mm_struct *mm, int member)
>  	return (unsigned long)val;
>  }
>  
> -void mm_trace_rss_stat(int member, long count);
> +void mm_trace_rss_stat(struct mm_struct *mm, int member, long count);
>  
>  static inline void add_mm_counter(struct mm_struct *mm, int member, long value)
>  {
>  	long count = atomic_long_add_return(value, &mm->rss_stat.count[member]);
>  
> -	mm_trace_rss_stat(member, count);
> +	mm_trace_rss_stat(mm, member, count);
>  }
>  
>  static inline void inc_mm_counter(struct mm_struct *mm, int member)
>  {
>  	long count = atomic_long_inc_return(&mm->rss_stat.count[member]);
>  
> -	mm_trace_rss_stat(member, count);
> +	mm_trace_rss_stat(mm, member, count);
>  }
>  
>  static inline void dec_mm_counter(struct mm_struct *mm, int member)
>  {
>  	long count = atomic_long_dec_return(&mm->rss_stat.count[member]);
>  
> -	mm_trace_rss_stat(member, count);
> +	mm_trace_rss_stat(mm, member, count);
>  }
>  
>  /* Optimized variant when page is already known not to be PageAnon */
> diff --git a/include/linux/string.h b/include/linux/string.h
> index f516cec5277c..6b0e950701d0 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -261,6 +261,8 @@ int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
>  extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
>  				       const void *from, size_t available);
>  
> +int ptr_to_hashval(const void *ptr, unsigned long *hashval_out);
> +
>  /**
>   * strstarts - does @str start with @prefix?
>   * @str: string to examine
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index 5a0666bfcf85..ad7e642bd497 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -316,24 +316,50 @@ TRACE_EVENT(mm_page_alloc_extfrag,
>  		__entry->change_ownership)
>  );
>  
> +/*
> + * Required for uniquely and securely identifying mm in rss_stat tracepoint.
> + */
> +#ifndef __PTR_TO_HASHVAL
> +static unsigned int __maybe_unused mm_ptr_to_hash(const void *ptr)
> +{
> +	int ret;
> +	unsigned long hashval;
> +
> +	ret = ptr_to_hashval(ptr, &hashval);
> +	if (ret)
> +		return 0;
> +
> +	/* The hashed value is only 32-bit */
> +	return (unsigned int)hashval;
> +}
> +#define __PTR_TO_HASHVAL
> +#endif
> +
>  TRACE_EVENT(rss_stat,
>  
> -	TP_PROTO(int member,
> +	TP_PROTO(struct mm_struct *mm,
> +		int member,
>  		long count),
>  
> -	TP_ARGS(member, count),
> +	TP_ARGS(mm, member, count),
>  
>  	TP_STRUCT__entry(
> +		__field(unsigned int, mm_id)
> +		__field(unsigned int, curr)
>  		__field(int, member)
>  		__field(long, size)
>  	),
>  
>  	TP_fast_assign(
> +		__entry->mm_id = mm_ptr_to_hash(mm);
> +		__entry->curr = !!(current->mm == mm);
>  		__entry->member = member;
>  		__entry->size = (count << PAGE_SHIFT);
>  	),
>  
> -	TP_printk("member=%d size=%ldB",
> +	TP_printk("mm_id=%u curr=%d member=%d size=%ldB",
> +		__entry->mm_id,
> +		__entry->curr,
>  		__entry->member,
>  		__entry->size)
>  	);
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index dee8fc467fcf..401baaac1813 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -761,11 +761,34 @@ static int __init initialize_ptr_random(void)
>  early_initcall(initialize_ptr_random);
>  
>  /* Maps a pointer to a 32 bit unique identifier. */
> +int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
> +{
> +	const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";
> +	unsigned long hashval;
> +
> +	if (static_branch_unlikely(&not_filled_random_ptr_key))
> +		return -EAGAIN;
> +
> +#ifdef CONFIG_64BIT
> +	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
> +	/*
> +	 * Mask off the first 32 bits, this makes explicit that we have
> +	 * modified the address (and 32 bits is plenty for a unique ID).
> +	 */
> +	hashval = hashval & 0xffffffff;
> +#else
> +	hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
> +#endif
> +	*hashval_out = hashval;
> +	return 0;
> +}
> +
>  static char *ptr_to_id(char *buf, char *end, const void *ptr,
>  		       struct printf_spec spec)
>  {
>  	const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";
>  	unsigned long hashval;
> +	int ret;
>  
>  	/* When debugging early boot use non-cryptographically secure hash. */
>  	if (unlikely(debug_boot_weak_hash)) {
> @@ -773,22 +796,13 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
>  		return pointer_string(buf, end, (const void *)hashval, spec);
>  	}
>  
> -	if (static_branch_unlikely(&not_filled_random_ptr_key)) {
> +	ret = ptr_to_hashval(ptr, &hashval);
> +	if (ret) {

This is a hot path (used in trace_printk()), and you just turned a
static_branch into a function call.

Can we make a __ptr_to_hashval() static inline, and have
ptr_to_hashval() call that, but use the static inline here, where the
static_branch gets called directly here?

-- Steve


>  		spec.field_width = 2 * sizeof(ptr);
>  		/* string length must be less than default_width */
>  		return error_string(buf, end, str, spec);
>  	}
>  
> -#ifdef CONFIG_64BIT
> -	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
> -	/*
> -	 * Mask off the first 32 bits, this makes explicit that we have
> -	 * modified the address (and 32 bits is plenty for a unique ID).
> -	 */
> -	hashval = hashval & 0xffffffff;
> -#else
> -	hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
> -#endif
>  	return pointer_string(buf, end, (const void *)hashval, spec);
>  }
>  
> diff --git a/mm/memory.c b/mm/memory.c
> index 7596d625ebd1..d3c9784e6dc1 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -154,9 +154,9 @@ static int __init init_zero_pfn(void)
>  }
>  core_initcall(init_zero_pfn);
>  
> -void mm_trace_rss_stat(int member, long count)
> +void mm_trace_rss_stat(struct mm_struct *mm, int member, long count)
>  {
> -	trace_rss_stat(member, count);
> +	trace_rss_stat(mm, member, count);
>  }
>  
>  #if defined(SPLIT_RSS_COUNTING)