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From: Steven Rostedt <rostedt@goodmis.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Jason Baron <jbaron@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH 0/5 v2] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops
Date: Wed, 01 Feb 2012 10:21:37 -0500	[thread overview]
Message-ID: <1328109697.5882.65.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <20120201080539.GA11770@elte.hu>

On Wed, 2012-02-01 at 09:05 +0100, Ingo Molnar wrote:
> * Steven Rostedt <rostedt@goodmis.org> wrote:

> It would be better to make this a regular commit, this kind of 
> diagnostics obviously makes sense. That way i could pull in your 
> updated branch for more testing.


Ingo,

I added the below patch on top of my previous pull request. If you run
this on the box that failed, it should give us a little more info.

Thanks!

Please pull the latest tip/perf/jump-label-3 tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/perf/jump-label-3

Head SHA1: abdefd743e4a28f11bcd38a441253f01dafea03e


Steven Rostedt (1):
      x86/jump lables: Show where and what was wrong on errors

----
 arch/x86/kernel/jump_label.c |   31 +++++++++++++++++++++----------
 1 files changed, 21 insertions(+), 10 deletions(-)
---------------------------
commit abdefd743e4a28f11bcd38a441253f01dafea03e
Author: Steven Rostedt <srostedt@redhat.com>
Date:   Wed Feb 1 09:59:24 2012 -0500

    x86/jump lables: Show where and what was wrong on errors
    
    When modifying text sections for jump labels, a paranoid check is
    performed. If the check fails, the system "bugs". But why it failed
    is not shown.
    
    The BUG_ON()s in the jump label update code is replaced with bug_at(ip).
    This is a function that will show what pointer failed, and what was
    at the location of the failure that made jump label panic.
    
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index 7112a27..2839524 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -32,6 +32,18 @@ union jump_code_union {
 	} __packed;
 };
 
+static void bug_at(unsigned char *ip, int line)
+{
+	/*
+	 * The location is not an op that we were expecting.
+	 * Something went wrong. Crash the box, as something could be
+	 * corrupting the kernel.
+	 */
+	printk("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n",
+	       ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line);
+	BUG();
+}
+
 static void __jump_label_transform(struct jump_entry *entry,
 				   enum jump_label_type type,
 				   void *(*poker)(void *, const void *, size_t),
@@ -59,12 +71,7 @@ static void __jump_label_transform(struct jump_entry *entry,
 			code.jump = 0xe9;
 			code.offset = entry->target - (entry->code + size);
 		} else
-			/*
-			 * The location is not a nop that we were expecting,
-			 * something went wrong. Crash the box, as something could be
-			 * corrupting the kernel.
-			 */
-			BUG();
+			bug_at(ip, __LINE__);
 	} else {
 		/*
 		 * We are disabling this jump label. If it is not what
@@ -78,7 +85,8 @@ static void __jump_label_transform(struct jump_entry *entry,
 				return;
 
 			/* We are initializing from the default nop */
-			BUG_ON(memcmp(ip, default_nop, 5) != 0);
+			if (unlikely(memcmp(ip, default_nop, 5) != 0))
+				bug_at(ip, __LINE__);
 
 			/* Set to the ideal nop */
 			size = JUMP_LABEL_NOP_SIZE;
@@ -91,7 +99,9 @@ static void __jump_label_transform(struct jump_entry *entry,
 			code.jump = 0xe9;
 			code.offset = entry->target -
 				(entry->code + JUMP_LABEL_NOP_SIZE);
-			BUG_ON(memcmp(ip, &code, 5) != 0);
+
+			if (unlikely(memcmp(ip, &code, 5) != 0))
+				bug_at(ip, __LINE__);
 
 			size = JUMP_LABEL_NOP_SIZE;
 			memcpy(&code, ideal_nops[NOP_ATOMIC5], size);
@@ -101,13 +111,14 @@ static void __jump_label_transform(struct jump_entry *entry,
 			/* Had better be a 2 byte jmp */
 			code.jump_short = 0xeb;
 			code.offset = entry->target - (entry->code + 2);
-			BUG_ON(memcmp(ip, &code, 2) != 0);
+			if (unlikely(memcmp(ip, &code, 2) != 0))
+				bug_at(ip, __LINE__);
 
 			size = 2;
 			memcpy(&code, nop_short, size);
 		} else
 			/* The code was not what we expected!  */
-			BUG();
+			bug_at(ip, __LINE__);
 	}
 
 	(*poker)(ip, &code, size);



  parent reply	other threads:[~2012-02-01 15:21 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-28 16:09 [PATCH 0/5 v2] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops Steven Rostedt
2012-01-28 16:09 ` [PATCH 1/5 v2] x86/jump-label: Use best default nops for inital jump label calls Steven Rostedt
2012-01-28 16:09 ` [PATCH 2/5 v2] x86/jump-label: Do not bother updating nops if they are correct Steven Rostedt
2012-01-28 16:09 ` [PATCH 3/5 v2] x86/jump-label: Add safety checks to jump label conversions Steven Rostedt
2012-01-28 16:09 ` [PATCH 4/5 v2] jump labels: Add infrastructure to update jump labels at compile time Steven Rostedt
2012-01-28 16:09 ` [PATCH 5/5 v2] x86/jump labels: Use etiher 5 byte or 2 byte jumps Steven Rostedt
2012-01-30 14:48 ` [PATCH 0/5 v2] [GIT PULL] x86/jump label: Paranoid checks and 2 or 5 byte nops Ingo Molnar
2012-01-30 15:07   ` Steven Rostedt
2012-01-31 19:48     ` Ingo Molnar
2012-02-01  5:08       ` Steven Rostedt
2012-02-01  8:05         ` Ingo Molnar
2012-02-01 13:20           ` Steven Rostedt
2012-02-01 15:21           ` Steven Rostedt [this message]
2012-02-02 13:51             ` Ingo Molnar
2012-02-02 14:10               ` H. Peter Anvin
2012-02-02 14:31                 ` Steven Rostedt
2012-02-02 22:04                   ` Steven Rostedt
2012-02-02 22:07                     ` H. Peter Anvin
2012-02-02 22:53                       ` Steven Rostedt
2012-02-03  7:36                   ` Ingo Molnar
2012-02-03 13:31                     ` Steven Rostedt
2012-02-05 11:47                       ` Ingo Molnar

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