sched/preempt, futex: Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly

David Hildenbrand · Ingo Molnar · commit d9b9ff8c1889 · 2015-05-19T08:39:16.000+02:00
Let's explicitly disable/enable preemption in the !CONFIG_SMP version of futex_atomic_cmpxchg_inatomic(), to prepare for pagefault_disable() not touching preemption anymore. This is needed for this function to be callable from both, atomic and non-atomic context. Otherwise we might break mutual exclusion when relying on a get_user()/ put_user() implementation. Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: David.Laight@ACULAB.COM Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: airlied@linux.ie Cc: akpm@linux-foundation.org Cc: benh@kernel.crashing.org Cc: bigeasy@linutronix.de Cc: borntraeger@de.ibm.com Cc: daniel.vetter@intel.com Cc: heiko.carstens@de.ibm.com Cc: herbert@gondor.apana.org.au Cc: hocko@suse.cz Cc: hughd@google.com Cc: mst@redhat.com Cc: paulus@samba.org Cc: ralf@linux-mips.org Cc: schwidefsky@de.ibm.com Cc: yang.shi@windriver.com Link: http://lkml.kernel.org/r/1431359540-32227-10-git-send-email-dahi@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/include/asm-generic/futex.h b/include/asm-generic/futex.h
@@ -107,13 +107,15 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 {
 	u32 val;
 
+	preempt_disable();
 	if (unlikely(get_user(val, uaddr) != 0))
 		return -EFAULT;
 
 	if (val == oldval && unlikely(put_user(newval, uaddr) != 0))
 		return -EFAULT;
 
 	*uval = val;
+	preempt_enable();
 
 	return 0;
 }

Original file line number	Diff line number	Diff line change
`@@ -107,13 +107,15 @@ futex_atomic_cmpxchg_inatomic(u32 uval, u32 __user uaddr,`
`107`	`107`	`{`
`108`	`108`	`u32 val;`
`109`	`109`
	`110`	`+ preempt_disable();`
`110`	`111`	`if (unlikely(get_user(val, uaddr) != 0))`
`111`	`112`	`return -EFAULT;`
`112`	`113`
`113`	`114`	`if (val == oldval && unlikely(put_user(newval, uaddr) != 0))`
`114`	`115`	`return -EFAULT;`
`115`	`116`
`116`	`117`	`*uval = val;`
	`118`	`+ preempt_enable();`
`117`	`119`
`118`	`120`	`return 0;`
`119`	`121`	`}`