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DateSun, 17 Nov 2002 22:46:13 -0800
FromUlrich Drepper <>
SubjectRe: [patch] threading fix, tid-2.5.47-A3
Linus Torvalds wrote:

> I'm convinced. However, I still want som elargely cosmetic changes to the
> patch, Ingo:
> [...]

I'm not Ingo but changing the patch seemed easy enough to do, even for
me. I append the patch below. It is not meant for inclusion since
there is onw more problem to solve. Ingo patch had another bug. The
user_tid field in the child didn't get set if CLONE_CHILD_CLEARTID was
set. This obviously has bad results.

I've changed the test to read

+ if (clone_flags & (CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID))
which works for me. But since in schedule_tail() the code reads

+ if (current->user_tid)
+ put_user(current->pid, current->user_tid);
this enables writing the TID even if CLONE_CHILD_SETTID isn't set. The
question is: how to access the clone flag information in the child?

Anyway, since this distinction isn't important for my tests I've applied
the attached patch and all runs fine.

--
--------------. ,-. 444 Castro Street
Ulrich Drepper \ ,-----------------' \ Mountain View, CA 94041 USA
Red Hat `--' drepper at redhat.com `------------------------------ linux-2.5/arch/i386/kernel/entry.S.tid 2002-11-17 16:11:26.000000000 -0800
+++ linux-2.5/arch/i386/kernel/entry.S 2002-11-17 21:56:18.000000000 -0800
@@ -193,10 +193,8 @@


ENTRY(ret_from_fork)
-#if CONFIG_SMP || CONFIG_PREEMPT
# NOTE: this function takes a parameter but it's unused on x86.
call schedule_tail
-#endif
GET_THREAD_INFO(%ebx)
jmp syscall_exit

--- linux-2.5/include/linux/sched.h.tid 2002-11-17 16:11:26.000000000 -0800
+++ linux-2.5/include/linux/sched.h 2002-11-17 22:04:56.000000000 -0800
@@ -46,10 +46,11 @@
#define CLONE_NEWNS 0x00020000 /* New namespace group? */
#define CLONE_SYSVSEM 0x00040000 /* share system V SEM_UNDO semantics */
#define CLONE_SETTLS 0x00080000 /* create a new TLS for the child */
-#define CLONE_SETTID 0x00100000 /* write the TID back to userspace */
-#define CLONE_CLEARTID 0x00200000 /* clear the userspace TID */
+#define CLONE_PARENT_SETTID 0x00100000 /* write the TID back to userspace */
+#define CLONE_CHILD_CLEARTID 0x00200000 /* clear the userspace TID */
#define CLONE_DETACHED 0x00400000 /* parent wants no child-exit signal */
#define CLONE_UNTRACED 0x00800000 /* set if the tracing process can't force CLONE_PTRACE on this clone */
+#define CLONE_CHILD_SETTID 0x01000000 /* set the TID in the child */

/*
* List of flags we want to share for kernel threads,
@@ -332,7 +333,7 @@

wait_queue_head_t wait_chldexit; /* for wait4() */
struct completion *vfork_done; /* for vfork() */
- int *user_tid; /* for CLONE_CLEARTID */
+ int *user_tid; /* for CLONE_[SET|CLEAR]TID */

unsigned long rt_priority;
unsigned long it_real_value, it_prof_value, it_virt_value;
--- linux-2.5/kernel/sched.c.tid 2002-11-17 16:11:26.000000000 -0800
+++ linux-2.5/kernel/sched.c 2002-11-17 21:59:58.000000000 -0800
@@ -503,12 +503,17 @@
* schedule_tail - first thing a freshly forked thread must call.
* @prev: the thread we just switched away from.
*/
-#if CONFIG_SMP || CONFIG_PREEMPT
+asmlinkage void FASTCALL(schedule_tail(task_t *prev));
asmlinkage void schedule_tail(task_t *prev)
{
finish_arch_switch(this_rq(), prev);
+
+ /*
+ * Does the child thread/process want to be notified of the TID/PID?
+ */
+ if (current->user_tid)
+ put_user(current->pid, current->user_tid);
}
-#endif

/*
* context_switch - switch to the new MM and the new
--- linux-2.5/kernel/fork.c.tid 2002-11-17 16:11:26.000000000 -0800
+++ linux-2.5/kernel/fork.c 2002-11-17 22:06:00.000000000 -0800
@@ -822,18 +822,15 @@
retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
if (retval)
goto bad_fork_cleanup_namespace;
- /*
- * Notify the child of the TID?
- */
retval = -EFAULT;
- if (clone_flags & CLONE_SETTID)
+ if (clone_flags & CLONE_PARENT_SETTID)
if (put_user(p->pid, user_tid))
goto bad_fork_cleanup_namespace;
-
/*
- * Does the userspace VM want the TID cleared on mm_release()?
+ * Does the userspace VM want the TID set in the child's
+ * address space and it cleared on mm_release()?
*/
- if (clone_flags & CLONE_CLEARTID)
+ if (clone_flags & (CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID))
p->user_tid = user_tid;

/*
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