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[PATCH] pi-futex: robust-futex exit

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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>
This commit is contained in:
Ingo Molnar
2006-07-29 05:17:57 +02:00
committed by Linus Torvalds
parent 627371d73c
commit e3f2ddeac7
3 changed files with 89 additions and 39 deletions
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34
kernel/futex_compat.c
View File

@ -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 @@ void compat_exit_robust_list(struct task_struct *curr)
{
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 @@ void compat_exit_robust_list(struct task_struct *curr)
* 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 @@ void compat_exit_robust_list(struct task_struct *curr)
*/
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:
*/