Robust Futex update

Ingo,
   here 's a patch for 2.6.14-rc4-rt1 that fixes two things:

1) Deregister futex returns -EBUSY instead of -EINVAL if a thread tries to deregister a pthread_mutex that another thread has locked.

2) Make the fast path robust. If a pthread_mutex is only locked in user space we need to clear the owner when the thread dies. This makes both the 'rt_mutex is locked in the kernel' and the 'pthread_mutex is only locked in user space'

paths robust.

David

Index: linux-2.6.13/kernel/futex.c
===================================================================
--- linux-2.6.13.orig/kernel/futex.c
+++ linux-2.6.13/kernel/futex.c
@@ -1354,18 +1354,25 @@ static void find_owned_futex(struct vm_a
 		if (uaddr == 0)
 			continue;
 
+		up(&mapping->robust_sem);
+		up_read(&current->mm->mmap_sem);
+		value = futex_get_user(uaddr);
+		if (this->futex_mutex.mutex_attr & FUTEX_ATTR_ROBUST)
+			value |= FUTEX_OWNER_DIED;
 		if (rt_mutex_owned_by(&this->futex_mutex, ti)) {
-			up(&mapping->robust_sem);
-			up_read(&current->mm->mmap_sem);
-			if (this->futex_mutex.mutex_attr & FUTEX_ATTR_ROBUST) {
-	 			value = futex_get_user(uaddr);
-				value |= FUTEX_OWNER_DIED;
- 				futex_put_user(value, uaddr);
-			}
+			futex_put_user(value, uaddr);
 			up_futex(&this->futex_mutex);
-			down(&mapping->robust_sem);
-			down_read(&current->mm->mmap_sem);
+		} else if ((value & FUTEX_PID) == current->pid) {
+			/*
+			 * this bit is for the fast path.  If the lock is only
+			 * locked in user space wee need to unlock it
+			 * for the exiting thread.
+			 */
+			value &= ~FUTEX_PID;
+			futex_put_user(value, uaddr);
 		}
+		down(&mapping->robust_sem);
+		down_read(&current->mm->mmap_sem);
 	}
 
 	up(&mapping->robust_sem);
@@ -1524,7 +1531,7 @@ static int futex_deregister(unsigned lon
 			if (rt_mutex_owned_by(&this->futex_mutex, ti)) {
 				up_futex(&this->futex_mutex);
 			} else if (rt_mutex_owner(&this->futex_mutex) != NULL) {
-				ret = -EINVAL;
+				ret = -EBUSY;
 				break;
 			}
 			list_del(&this->list);
Index: linux-2.6.13/include/linux/futex.h
===================================================================
--- linux-2.6.13.orig/include/linux/futex.h
+++ linux-2.6.13/include/linux/futex.h
@@ -1,8 +1,6 @@
 #ifndef _LINUX_FUTEX_H
 #define _LINUX_FUTEX_H
 
-#include <linux/fs.h>
-
 /* Second argument to futex syscall */
 
 
Index: linux-2.6.13/kernel/rt.c
===================================================================
--- linux-2.6.13.orig/kernel/rt.c
+++ linux-2.6.13/kernel/rt.c
@@ -47,6 +47,7 @@
 #include <linux/syscalls.h>
 #include <linux/interrupt.h>
 #include <linux/plist.h>
+#include <linux/fs.h>
 #include <linux/futex.h>
 
 #define CAPTURE_LOCK

---

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    • From: Ingo Molnar <[email protected]>
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    • From: Ingo Molnar <[email protected]>

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