From edbd0387f3249cc7e102f86d4852a9a9f3bb1305 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Sun, 27 Nov 2022 22:49:38 +1000 Subject: [PATCH] powerpc: copy_thread add a back chain to the switch stack frame Stack unwinders need LR and the back chain as a minimum. The switch stack uses regs->nip for its return pointer rather than lrsave, so that was not set in the fork frame, and neither was the back chain. This change sets those fields in the stack. With this and the previous change, a stack trace in the switch or interrupt stack goes from looking like this: Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries Modules linked in: CPU: 3 PID: 90 Comm: systemd Not tainted NIP: c000000000011060 LR: c000000000010f68 CTR: 0000000000007fff [ ... regs ... ] NIP [c000000000011060] _switch+0x160/0x17c LR [c000000000010f68] _switch+0x68/0x17c Call Trace: To this: Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries CPU: 0 PID: 93 Comm: systemd Not tainted NIP: c000000000011060 LR: c000000000010f68 CTR: 0000000000007fff [ ... regs ... ] NIP [c000000000011060] _switch+0x160/0x17c LR [c000000000010f68] _switch+0x68/0x17c Call Trace: [c000000005a93e10] [c00000000000cdbc] ret_from_fork_scv+0x0/0x54 --- interrupt: 3000 at 0x7fffa72f56d8 NIP: 00007fffa72f56d8 LR: 0000000000000000 CTR: 0000000000000000 [ ... regs ... ] NIP [00007fffa72f56d8] 0x7fffa72f56d8 LR [0000000000000000] 0x0 --- interrupt: 3000 Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20221127124942.1665522-14-npiggin@gmail.com --- arch/powerpc/kernel/process.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 6b1d80bd370e..096b6ea52378 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1810,7 +1810,9 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) * do some house keeping and then return from the fork or clone * system call, using the stack frame created above. */ + ((unsigned long *)sp)[STACK_FRAME_LR_SAVE] = (unsigned long)f; sp -= STACK_SWITCH_FRAME_SIZE; + ((unsigned long *)sp)[0] = sp + STACK_SWITCH_FRAME_SIZE; kregs = (struct pt_regs *)(sp + STACK_SWITCH_FRAME_REGS); p->thread.ksp = sp;