LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: tip-bot for Andy Lutomirski <tipbot@zytor.com>,
	linux-tip-commits@vger.kernel.org, luto@kernel.org,
	hpa@zytor.com, dvlasenk@redhat.com, linux-kernel@vger.kernel.org,
	jann@thejh.net, peterz@infradead.org,
	torvalds@linux-foundation.org, brgerst@gmail.com,
	tglx@linutronix.de, bp@alien8.de
Subject: [PATCH] x86/dumpstack: remove NULL task pointer convention
Date: Fri, 16 Sep 2016 08:05:20 -0500
Message-ID: <20160916130520.pecrue7yhj5547bs@treble> (raw)
In-Reply-To: <20160916125754.GA10184@gmail.com>

On Fri, Sep 16, 2016 at 02:57:54PM +0200, Ingo Molnar wrote:
> 
> * Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> 
> > On Fri, Sep 16, 2016 at 06:55:57AM -0500, Josh Poimboeuf wrote:
> > > On Fri, Sep 16, 2016 at 02:17:46AM -0700, tip-bot for Andy Lutomirski wrote:
> > > > Commit-ID:  1959a60182f48879635812a03a99c02231ea8677
> > > > Gitweb:     http://git.kernel.org/tip/1959a60182f48879635812a03a99c02231ea8677
> > > > Author:     Andy Lutomirski <luto@kernel.org>
> > > > AuthorDate: Thu, 15 Sep 2016 22:45:45 -0700
> > > > Committer:  Ingo Molnar <mingo@kernel.org>
> > > > CommitDate: Fri, 16 Sep 2016 09:18:53 +0200
> > > > 
> > > > x86/dumpstack: Pin the target stack when dumping it
> > > > 
> > > > Specifically, pin the stack in save_stack_trace_tsk() and
> > > > show_trace_log_lvl().
> > > > 
> > > > This will prevent a crash if the target task dies before or while
> > > > dumping its stack once we start freeing task stacks early.
> > > 
> > > This causes a hang:
> > 
> > The problem is that show_stack_log_lvl() can be called with a NULL
> > task_struct pointer to indicate 'current'.
> 
> Could you please send a quick fix that addresses the hang by turning the NULL into 
> 'current' or so?
> 
> > No idea why that convention exists -- IMO we should just require the
> > caller to pass 'current' directly.
> 
> For hysterical raisins I believe. It appears just a single caller passes 
> non-current. Feel free to change this.

I've verified that this fixes it.  It can be applied before Andy's patch
(or after if you don't want to rebase).

---

From: Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH] x86/dumpstack: remove NULL task pointer convention

show_stack_log_lvl() and friends allow a NULL pointer for the
task_struct to indicate the current task.  This creates confusion and
can cause sneaky bugs.

Instead require the caller to pass 'current' directly.

This only changes the internal workings of the dumpstack code.  The
dump_trace() and show_stack() interfaces still allow a NULL task
pointer.  Those interfaces should also probably be fixed as well.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/include/asm/stacktrace.h | 4 ++--
 arch/x86/kernel/dumpstack.c       | 4 +++-
 arch/x86/kernel/dumpstack_32.c    | 2 +-
 arch/x86/kernel/dumpstack_64.c    | 2 +-
 4 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index 780a83e..ed2be1b 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -94,7 +94,7 @@ get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
 	if (regs)
 		return (unsigned long *)regs->bp;
 
-	if (!task || task == current)
+	if (task == current)
 		return __builtin_frame_address(0);
 
 	return (unsigned long *)((struct inactive_task_frame *)task->thread.sp)->bp;
@@ -113,7 +113,7 @@ get_stack_pointer(struct task_struct *task, struct pt_regs *regs)
 	if (regs)
 		return (unsigned long *)kernel_stack_pointer(regs);
 
-	if (!task || task == current)
+	if (task == current)
 		return __builtin_frame_address(0);
 
 	return (unsigned long *)task->thread.sp;
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index aa208e5..e0648f7 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -175,11 +175,13 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 {
 	unsigned long bp = 0;
 
+	task = task ? : current;
+
 	/*
 	 * Stack frames below this one aren't interesting.  Don't show them
 	 * if we're printing for %current.
 	 */
-	if (!sp && (!task || task == current)) {
+	if (!sp && task == current) {
 		sp = get_stack_pointer(current, NULL);
 		bp = (unsigned long)get_frame_pointer(current, NULL);
 	}
diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 2d65cfa..ded285c 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -200,7 +200,7 @@ void show_regs(struct pt_regs *regs)
 		u8 *ip;
 
 		pr_emerg("Stack:\n");
-		show_stack_log_lvl(NULL, regs, NULL, 0, KERN_EMERG);
+		show_stack_log_lvl(current, regs, NULL, 0, KERN_EMERG);
 
 		pr_emerg("Code:");
 
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 8cb6004..4fac236 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -273,7 +273,7 @@ void show_regs(struct pt_regs *regs)
 		u8 *ip;
 
 		printk(KERN_DEFAULT "Stack:\n");
-		show_stack_log_lvl(NULL, regs, NULL, 0, KERN_DEFAULT);
+		show_stack_log_lvl(current, regs, NULL, 0, KERN_DEFAULT);
 
 		printk(KERN_DEFAULT "Code: ");
 
-- 
2.7.4

  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-16  5:45 [PATCH v2 0/8] thread_info cleanups and stack caching Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 1/8] x86/entry/64: Fix a minor comment rebase error Andy Lutomirski
2016-09-16  9:16   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 2/8] sched: Add try_get_task_stack() and put_task_stack() Andy Lutomirski
2016-09-16  9:16   ` [tip:x86/asm] sched/core: " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 3/8] kthread: to_live_kthread() needs try_get_task_stack() Andy Lutomirski
2016-09-16  9:17   ` [tip:x86/asm] kthread: Pin the stack via try_get_task_stack()/put_task_stack() in to_live_kthread() function tip-bot for Oleg Nesterov
2016-09-16  5:45 ` [PATCH v2 4/8] x86/dumpstack: Pin the target stack when dumping it Andy Lutomirski
2016-09-16  9:17   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16 11:55     ` Josh Poimboeuf
2016-09-16 12:28       ` Josh Poimboeuf
2016-09-16 12:57         ` Ingo Molnar
2016-09-16 13:05           ` Josh Poimboeuf [this message]
2016-09-16  5:45 ` [PATCH v2 5/8] x86/process: Pin the target stack in get_wchan() Andy Lutomirski
2016-09-16  9:18   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 6/8] lib/syscall: Pin the task stack in collect_syscall() Andy Lutomirski
2016-09-16  9:18   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 7/8] sched: Free the stack early if CONFIG_THREAD_INFO_IN_TASK Andy Lutomirski
2016-09-16  9:19   ` [tip:x86/asm] sched/core: " tip-bot for Andy Lutomirski
2016-09-16  5:45 ` [PATCH v2 8/8] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski
2016-09-16  9:19   ` [tip:x86/asm] fork: Optimize task creation by caching two thread stacks per CPU if CONFIG_VMAP_STACK=y tip-bot for Andy Lutomirski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20160916130520.pecrue7yhj5547bs@treble \
    --to=jpoimboe@redhat.com \
    --cc=bp@alien8.de \
    --cc=brgerst@gmail.com \
    --cc=dvlasenk@redhat.com \
    --cc=hpa@zytor.com \
    --cc=jann@thejh.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-tip-commits@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=tipbot@zytor.com \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git