powerpc: Call restore_sprs() before _switch()

commit 152d523e6307 ("powerpc: Create context switch helpers save_sprs()
and restore_sprs()") moved the restore of SPRs after the call to _switch().

There is an issue with this approach - new tasks do not return through
_switch(), they are set up by copy_thread() to directly return through
ret_from_fork() or ret_from_kernel_thread(). This means restore_sprs() is
not getting called for new tasks.

Fix this by moving restore_sprs() before _switch().

Fixes: 152d523e6307 ("powerpc: Create context switch helpers save_sprs() and restore_sprs()")
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 1eeda3b80b65b48772f1b0b739c4782cd80218d8..9da7b5f0c3a55fa630232e98b61ed3c21698770b 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -971,14 +971,17 @@ struct task_struct *__switch_to(struct task_struct *prev,
 
        tm_recheckpoint_new_task(new);
 
-       last = _switch(old_thread, new_thread);
-
-       /* Need to recalculate these after calling _switch() */
-       old_thread = &last->thread;
-       new_thread = &current->thread;
-
+       /*
+        * Call restore_sprs() before calling _switch(). If we move it after
+        * _switch() then we miss out on calling it for new tasks. The reason
+        * for this is we manually create a stack frame for new tasks that
+        * directly returns through ret_from_fork() or
+        * ret_from_kernel_thread(). See copy_thread() for details.
+        */
        restore_sprs(old_thread, new_thread);
 
+       last = _switch(old_thread, new_thread);
+
 #ifdef CONFIG_PPC_BOOK3S_64
        if (current_thread_info()->local_flags & _TLF_LAZY_MMU) {
                current_thread_info()->local_flags &= ~_TLF_LAZY_MMU;