linux-kernel - copy_process() && ti->flags (Was: PT

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Message-ID: <20090426231820.GB6580@redhat.com>
Date:	Mon, 27 Apr 2009 01:18:20 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jeff Dike <jdike@...toit.com>, Roland McGrath <roland@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: copy_process() && ti->flags (Was: PT_DTRACE && uml)

On 04/27, Oleg Nesterov wrote:
>
> Do you see other problems with this patch? (uncompiled, untested).

dup_task_struct()->setup_thread_stack() copies parent's ti->flags.

Why? Which flags should be actually copied? I must have missed
something, but whats wrong with the patch below?

OK, it is wrong. On x86 we should at least copy TIF_IA32. But
why should we copy, say, TIF_DEBUG?

Actually, I don't understand why don't we use TS_IA32 instead of
TIF_IA32. Only current can change this flag, perhaps it makes sense
to move it in thread_info->status.

copy_process()->clear_tsk_thread_flag(TIF_SIGPENDING) looks unneeded
in any case...

Oleg.


--- kernel/fork.c
+++ kernel/fork.c
@@ -241,6 +241,7 @@ static struct task_struct *dup_task_stru
 		goto out;
 
 	setup_thread_stack(tsk, orig);
+	ti->flags = 0;
 	stackend = end_of_stack(tsk);
 	*stackend = STACK_END_MAGIC;	/* for overflow detection */
 
@@ -1027,7 +1028,6 @@ static struct task_struct *copy_process(
 	p->vfork_done = NULL;
 	spin_lock_init(&p->alloc_lock);
 
-	clear_tsk_thread_flag(p, TIF_SIGPENDING);
 	init_sigpending(&p->pending);
 
 	p->utime = cputime_zero;
@@ -1163,14 +1163,6 @@ static struct task_struct *copy_process(
 	if ((clone_flags & (CLONE_VM|CLONE_VFORK)) == CLONE_VM)
 		p->sas_ss_sp = p->sas_ss_size = 0;
 
-	/*
-	 * Syscall tracing should be turned off in the child regardless
-	 * of CLONE_PTRACE.
-	 */
-	clear_tsk_thread_flag(p, TIF_SYSCALL_TRACE);
-#ifdef TIF_SYSCALL_EMU
-	clear_tsk_thread_flag(p, TIF_SYSCALL_EMU);
-#endif
 	clear_all_latency_tracing(p);
 
 	/* ok, now we should be set up.. */

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