Subject: [PATCH] MIPS: only process negative stack offsets on stack traces
From: Felix Fietkau <[email-masked]>
Date: Wed, 18 Apr 2018 10:50:05 +0200

Fixes endless back traces in cases where the compiler emits a stack
pointer increase in a branch delay slot (probably for some form of
function return).

[    3.475442] BUG: MAX_STACK_TRACE_ENTRIES too low!
[    3.480070] turning off the locking correctness validator.
[    3.485521] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.14.34 #0
[    3.491475] Stack : 00000000 00000000 00000000 00000000 80e0fce2 00000034 00000000 00000000
[    3.499764]         87c3838c 80696377 8061047c 00000000 00000001 00000001 87c2d850 6534689f
[    3.508059]         00000000 00000000 80e10000 00000000 00000000 000000cf 0000000f 00000000
[    3.516353]         00000000 806a0000 00076891 00000000 00000000 00000000 ffffffff 00000000
[    3.524648]         806c0000 00000004 80e10000 806a0000 00000003 80690000 00000000 80700000
[    3.532942]         ...
[    3.535362] Call Trace:
[    3.537818] [<80010a48>] show_stack+0x58/0x100
[    3.542207] [<804c2f78>] dump_stack+0xe8/0x170
[    3.546613] [<80079f90>] save_trace+0xf0/0x110
[    3.551010] [<8007b1ec>] mark_lock+0x33c/0x78c
[    3.555413] [<8007bf48>] __lock_acquire+0x2ac/0x1a08
[    3.560337] [<8007de60>] lock_acquire+0x64/0x8c
[    3.564846] [<804e1570>] _raw_spin_lock_irqsave+0x54/0x78
[    3.570186] [<801b618c>] kernfs_notify+0x94/0xac
[    3.574770] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.579257] [<801b618c>] kernfs_notify+0x94/0xac
[    3.583839] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.588329] [<801b618c>] kernfs_notify+0x94/0xac
[    3.592911] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.597401] [<801b618c>] kernfs_notify+0x94/0xac
[    3.601983] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.606473] [<801b618c>] kernfs_notify+0x94/0xac
[    3.611055] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.615545] [<801b618c>] kernfs_notify+0x94/0xac
[    3.620125] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.624619] [<801b618c>] kernfs_notify+0x94/0xac
[    3.629197] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.633691] [<801b618c>] kernfs_notify+0x94/0xac
[    3.638269] [<801b7b10>] sysfs_notify+0x74/0xa0
[    3.642763] [<801b618c>] kernfs_notify+0x94/0xac

Signed-off-by: Felix Fietkau <[email-masked]>
---

--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -380,6 +380,8 @@ static inline int is_sp_move_ins(union m
 
 	if (ip->i_format.opcode == addiu_op ||
 	    ip->i_format.opcode == daddiu_op) {
+		if (ip->i_format.simmediate > 0)
+			return 0;
 		*frame_size = -ip->i_format.simmediate;
 		return 1;
 	}