[PATCH] pi-futex: robust-futex exit
Fix robust PI-futexes to be properly unlocked on unexpected exit.
For this to work the kernel has to know whether a futex is a PI or a
non-PI one, because the semantics are different. Since the space in
relevant glibc data structures is extremely scarce, the best solution is
to encode the 'PI' information in bit 0 of the robust list pointer.
Existing (non-PI) glibc robust futexes have this bit always zero, so the
ABI is kept. New glibc with PI-robust-futexes will set this bit.
Further fixes from Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index d1d92b4..d1aab1a 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -12,6 +12,23 @@
#include <asm/uaccess.h>
+
+/*
+ * Fetch a robust-list pointer. Bit 0 signals PI futexes:
+ */
+static inline int
+fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
+ compat_uptr_t *head, int *pi)
+{
+ if (get_user(*uentry, head))
+ return -EFAULT;
+
+ *entry = compat_ptr((*uentry) & ~1);
+ *pi = (unsigned int)(*uentry) & 1;
+
+ return 0;
+}
+
/*
* Walk curr->robust_list (very carefully, it's a userspace list!)
* and mark any locks found there dead, and notify any waiters.
@@ -22,17 +39,16 @@
{
struct compat_robust_list_head __user *head = curr->compat_robust_list;
struct robust_list __user *entry, *pending;
+ unsigned int limit = ROBUST_LIST_LIMIT, pi;
compat_uptr_t uentry, upending;
- unsigned int limit = ROBUST_LIST_LIMIT;
compat_long_t futex_offset;
/*
* Fetch the list head (which was registered earlier, via
* sys_set_robust_list()):
*/
- if (get_user(uentry, &head->list.next))
+ if (fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
return;
- entry = compat_ptr(uentry);
/*
* Fetch the relative futex offset:
*/
@@ -42,11 +58,11 @@
* Fetch any possibly pending lock-add first, and handle it
* if it exists:
*/
- if (get_user(upending, &head->list_op_pending))
+ if (fetch_robust_entry(&upending, &pending,
+ &head->list_op_pending, &pi))
return;
- pending = compat_ptr(upending);
if (upending)
- handle_futex_death((void *)pending + futex_offset, curr);
+ handle_futex_death((void *)pending + futex_offset, curr, pi);
while (compat_ptr(uentry) != &head->list) {
/*
@@ -55,15 +71,15 @@
*/
if (entry != pending)
if (handle_futex_death((void *)entry + futex_offset,
- curr))
+ curr, pi))
return;
/*
* Fetch the next entry in the list:
*/
- if (get_user(uentry, (compat_uptr_t *)&entry->next))
+ if (fetch_robust_entry(&uentry, &entry,
+ (compat_uptr_t *)&entry->next, &pi))
return;
- entry = compat_ptr(uentry);
/*
* Avoid excessively long or circular lists:
*/