Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1441578

[PATCH RT 07/14] sched,preempt: Fix preempt_count manipulations

Show all headers | View raw

3.14.72-rt76-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

Vikram reported that his ARM64 compiler managed to 'optimize' away the
preempt_count manipulations in code like:

	preempt_enable_no_resched();
	put_user();
	preempt_disable();

Irrespective of that fact that that is horrible code that should be
fixed for many reasons, it does highlight a deficiency in the generic
preempt_count manipulators. As it is never right to combine/elide
preempt_count manipulations like this.

Therefore sprinkle some volatile in the two generic accessors to
ensure the compiler is aware of the fact that the preempt_count is
observed outside of the regular program-order view and thus cannot be
optimized away like this.

x86; the only arch not using the generic code is not affected as we
do all this in asm in order to use the segment base per-cpu stuff.

Cc: stable@vger.kernel.org
Cc: stable-rt@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: a787870924db ("sched, arch: Create asm/preempt.h")
Reported-by: Vikram Mulukutla <markivx@codeaurora.org>
Tested-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/asm-generic/preempt.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index 54352f4dde1a..65759d8b0b46 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -7,10 +7,10 @@
 
 static __always_inline int preempt_count(void)
 {
-	return current_thread_info()->preempt_count;
+	return READ_ONCE(current_thread_info()->preempt_count);
 }
 
-static __always_inline int *preempt_count_ptr(void)
+static __always_inline volatile int *preempt_count_ptr(void)
 {
 	return &current_thread_info()->preempt_count;
 }
-- 
2.8.1

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH RT 00/14] Linux 3.14.72-rt76-rc1 Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 14/14] Linux 3.14.72-rt76-rc1 Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 11/14] mm: perform lru_add_drain_all() remotely Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 10/14] locallock: add local_lock_on() Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 07/14] sched,preempt: Fix preempt_count manipulations Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 09/14] arm: lazy preempt: correct resched condition Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 08/14] kernel/printk: Dont try to print from IRQ/NMI region Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 04/14] list_bl: fixup bogus lockdep warning Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  [PATCH RT 03/14] net: dev: always take qdiscs busylock in __dev_xmit_skb() Steven Rostedt <rostedt@goodmis.org> - 2016-07-12 19:00 +0200
  Linux 3.14.72-rt76-rc2 Steven Rostedt <rostedt@goodmis.org> - 2016-07-13 01:30 +0200

csiph-web