[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>

diff --git a/arch/s390/kernel/head31.S b/arch/s390/kernel/head31.S
index 2ced846..602b508 100644 (file)
--- 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 65667b2..bdcb3f0 100644 (file)
--- 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