From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Masami Hiramatsu <mhiramat@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Andy Lutomirski <luto@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Namhyung Kim <namhyung@kernel.org>,
"Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: [RFC][PATCH 01/14 v2] function_graph: Convert ret_stack to a series of longs
Date: Fri, 24 May 2019 08:05:53 -0400 [thread overview]
Message-ID: <20190524080553.354f1cae@gandalf.local.home> (raw)
In-Reply-To: <20190524111144.GI2589@hirez.programming.kicks-ass.net>
On Fri, 24 May 2019 13:11:44 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, May 20, 2019 at 10:20:02AM -0400, Steven Rostedt wrote:
>
> > +#define FGRAPH_RET_SIZE (sizeof(struct ftrace_ret_stack))
> > +#define FGRAPH_RET_INDEX (ALIGN(FGRAPH_RET_SIZE, sizeof(long)) / sizeof(long))
>
> I think you want to write that like:
>
> BUILD_BUG_ON(sizeof(ftrace_ret_stack) % sizeof(long));
Sure.
>
> It'd be very weird for that sizeof not to be right.
Agreed, but I was paranoid. The BUILD_BUG_ON() would also work.
>
> > +#define SHADOW_STACK_SIZE (PAGE_SIZE)
>
> Do we really need that big a shadow stack?
Well, this is a sticky point. I allow up to 16 users at a time
(although I can't imagine more than 5, but you never know), and each
user adds a long and up to 4 more words (which is probably unlikely
anyway). And then we can have deep call stacks (we are getting deeper
each release it seems).
I figured, I start with a page size, and then in the future we can make
it dynamic, or shrink it if it proves to be too much.
>
> > +#define SHADOW_STACK_INDEX \
> > + (ALIGN(SHADOW_STACK_SIZE, sizeof(long)) / sizeof(long))
> > +/* Leave on a buffer at the end */
> > +#define SHADOW_STACK_MAX_INDEX (SHADOW_STACK_INDEX - FGRAPH_RET_INDEX)
> > +
> > +#define RET_STACK(t, index) ((struct ftrace_ret_stack *)(&(t)->ret_stack[index]))
> > +#define RET_STACK_INC(c) ({ c += FGRAPH_RET_INDEX; })
> > +#define RET_STACK_DEC(c) ({ c -= FGRAPH_RET_INDEX; })
>
> I'm thinking something like:
>
> #define RET_PUSH(s, val) \
> do { \
> (s) -= sizeof(val); \
> (typeof(val) *)(s) = val; \
> } while (0)
>
> #define RET_POP(s, type) \
> ({ \
> type *__ptr = (void *)(s); \
> (s) += sizeof(type); \
> *__ptr; \
> })
>
> Would me clearer?
Due to races with interrupts, and this not being an atomic operation, I
had to play tricks with moving the stack pointer and adding data to it.
So I wanted to keep the changing of the stack pointer and adding and
retrieving of the stack data separate.
Later patches remove the RET_STACK_INC/DEC() anyway.
Thanks for taking the time to look at these patches!
-- Steve
next prev parent reply other threads:[~2019-05-24 12:05 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 14:20 [RFC][PATCH 00/14 v2] function_graph: Rewrite to allow multiple users Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 01/14 v2] function_graph: Convert ret_stack to a series of longs Steven Rostedt
2019-05-24 11:11 ` Peter Zijlstra
2019-05-24 12:05 ` Steven Rostedt [this message]
2019-06-03 11:30 ` Masami Hiramatsu
2019-06-04 9:04 ` Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 02/14 v2] function_graph: Add an array structure that will allow multiple callbacks Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 03/14 v2] function_graph: Allow multiple users to attach to function graph Steven Rostedt
2019-05-24 11:26 ` Peter Zijlstra
2019-05-24 12:12 ` Steven Rostedt
2019-05-24 12:27 ` Peter Zijlstra
2019-05-24 12:57 ` Steven Rostedt
2019-05-27 10:10 ` Peter Zijlstra
2019-05-27 11:08 ` Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 04/14 v2] function_graph: Remove logic around ftrace_graph_entry and return Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 05/14 v2] ftrace/function_graph: Pass fgraph_ops to function graph callbacks Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 06/14 v2] ftrace: Allow function_graph tracer to be enabled in instances Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 07/14 v2] ftrace: Allow ftrace startup flags exist without dynamic ftrace Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 08/14 v2] function_graph: Have the instances use their own ftrace_ops for filtering Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 09/14 v2] function_graph: Add "task variables" per task for fgraph_ops Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 10/14 v2] function_graph: Move set_graph_function tests to shadow stack global var Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 11/14 v2] function_graph: Move graph depth stored data " Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 12/14 v2] function_graph: Move graph notrace bit " Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 13/14 v2] function_graph: Implement fgraph_reserve_data() and fgraph_retrieve_data() Steven Rostedt
2019-05-20 14:20 ` [RFC][PATCH 14/14 v2] function_graph: Add selftest for passing local variables Steven Rostedt
2019-05-22 14:19 ` [RFC][PATCH 00/14 v2] function_graph: Rewrite to allow multiple users Masami Hiramatsu
2019-05-22 14:40 ` Steven Rostedt
2019-05-29 6:47 ` Masami Hiramatsu
2019-05-29 9:25 ` Steven Rostedt
2019-05-30 9:29 ` Masami Hiramatsu
2019-06-08 6:23 ` Steven Rostedt
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