[S390] Initialize __LC_THREAD_INFO early.

"lockdep: Fix backtraces" reveales a bug in early setup code: when
lockdep tries to save a stack backtrace before setup_arch has been
called the lowcore pointer for the current thread info pointer isn't
initialized yet.
However our save stack backtrace code relies on it. If the pointer
isn't initialized the saved backtrace will have zero entries.
lockdep however relies (correctly) on the fact that that cannot
happen.
A write access to some random memory region is the result.

Fix this by initializing the thread info pointer early.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 2 insertions, 0 deletions

diff --git a/arch/s390/kernel/head31.S b/arch/s390/kernel/head31.S
index 2ced846065b7..602b508cd4c4 100644
--- a/arch/s390/kernel/head31.S
+++ b/arch/s390/kernel/head31.S
@@ -24,6 +24,7 @@ startup_continue:
 # Setup stack
 #
         l       %r15,.Linittu-.LPG1(%r13)
+        st      %r15,__LC_THREAD_INFO   # cache thread info in lowcore
         mvc     __LC_CURRENT(4),__TI_task(%r15)
         ahi     %r15,1<<(PAGE_SHIFT+THREAD_ORDER) # init_task_union+THREAD_SIZE
         st      %r15,__LC_KERNEL_STACK  # set end of kernel stack
diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S
index 65667b2e65ce..bdcb3f05bcd1 100644
--- a/arch/s390/kernel/head64.S
+++ b/arch/s390/kernel/head64.S
@@ -92,6 +92,7 @@ startup_continue:
 # Setup stack
 #
         larl    %r15,init_thread_union
+        stg     %r15,__LC_THREAD_INFO   # cache thread info in lowcore
         lg      %r14,__TI_task(%r15)    # cache current in lowcore
         stg     %r14,__LC_CURRENT
         aghi    %r15,1<<(PAGE_SHIFT+THREAD_ORDER) # init_task_union + THREAD_SIZE