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Subject[PATCH 6/7] uml: add arch_switch_to for newly forked thread
Date
From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Newly forked threads have no arch_switch_to_skas() called before their first
run, because when schedule() switches to them they're resumed in the body of
thread_wait() inside fork_handler() rather than in switch_threads() in
switch_to_skas().
Compensate this missing call.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

arch/um/kernel/skas/process_kern.c | 7 +++++++
arch/um/sys-i386/ptrace.c | 9 ++++++++-
arch/um/sys-i386/tls.c | 13 ++++++++++---
3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/um/kernel/skas/process_kern.c b/arch/um/kernel/skas/process_kern.c
index 38b1853..2135eaf 100644
--- a/arch/um/kernel/skas/process_kern.c
+++ b/arch/um/kernel/skas/process_kern.c
@@ -91,10 +91,17 @@ void fork_handler(int sig)
panic("blech");

schedule_tail(current->thread.prev_sched);
+
+ /* XXX: if interrupt_end() calls schedule, this call to
+ * arch_switch_to_skas isn't needed. We could want to apply this to
+ * improve performance. -bb */
+ arch_switch_to_skas(current->thread.prev_sched, current);
+
current->thread.prev_sched = NULL;

/* Handle any immediate reschedules or signals */
interrupt_end();
+
userspace(&current->thread.regs.regs);
}

diff --git a/arch/um/sys-i386/ptrace.c b/arch/um/sys-i386/ptrace.c
index b587b4b..ce71923 100644
--- a/arch/um/sys-i386/ptrace.c
+++ b/arch/um/sys-i386/ptrace.c
@@ -23,7 +23,14 @@ void arch_switch_to_tt(struct task_struc

void arch_switch_to_skas(struct task_struct *from, struct task_struct *to)
{
- arch_switch_tls_skas(from, to);
+ int err = arch_switch_tls_skas(from, to);
+ if (!err)
+ return;
+
+ if (err != -EINVAL)
+ printk(KERN_WARNING "arch_switch_tls_skas failed, errno %d, not EINVAL\n", -err);
+ else
+ printk(KERN_WARNING "arch_switch_tls_skas failed, errno = EINVAL\n");
}

int is_syscall(unsigned long addr)
diff --git a/arch/um/sys-i386/tls.c b/arch/um/sys-i386/tls.c
index e3c5bc5..2251654 100644
--- a/arch/um/sys-i386/tls.c
+++ b/arch/um/sys-i386/tls.c
@@ -70,8 +70,6 @@ static int get_free_idx(struct task_stru
return -ESRCH;
}

-#define O_FORCE 1
-
static inline void clear_user_desc(struct user_desc* info)
{
/* Postcondition: LDT_empty(info) returns true. */
@@ -84,6 +82,8 @@ static inline void clear_user_desc(struc
info->seg_not_present = 1;
}

+#define O_FORCE 1
+
static int load_TLS(int flags, struct task_struct *to)
{
int ret = 0;
@@ -162,7 +162,13 @@ void clear_flushed_tls(struct task_struc
* SKAS patch. */
int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
{
- return load_TLS(O_FORCE, to);
+ /* We have no need whatsoever to switch TLS for kernel threads; beyond
+ * that, that would also result in us calling os_set_thread_area with
+ * userspace_pid[cpu] == 0, which gives an error. */
+ if (likely(to->mm))
+ return load_TLS(O_FORCE, to);
+
+ return 0;
}

int arch_switch_tls_tt(struct task_struct *from, struct task_struct *to)
@@ -324,3 +330,4 @@ int ptrace_get_thread_area(struct task_s
out:
return ret;
}
+
-
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