The SAVE_SOME macro is used to save the execution context on all exceptions. If an exception occurs while executing user code, the stack is switched to the kernel's stack for the current task, and register $28 is switched to point to the current_thread_info, which is at the bottom of the stack region. If the exception occurs while executing kernel code, the stack is left, and this change ensures that register $28 is not updated. This is the correct behaviour when the kernel can be executing on the separate irq stack, because the thread_info will not be at the base of it. With this change, register $28 is only switched to it's kernel conventional usage of the currrent thread info pointer at the point at which execution enters kernel space. Doing it on every exception was redundant, but OK without an IRQ stack, but will be erroneous once that is introduced. Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxxxx> --- Changes in v3: Drop superfluous nop that would have been in delay slot with .set noreorder but is no longer required now that the code is .set reorder. Changes in v2: Drop .set reorder/noreorder when updating $28 arch/mips/include/asm/stackframe.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h index eebf39549606..2f182bdf024f 100644 --- a/arch/mips/include/asm/stackframe.h +++ b/arch/mips/include/asm/stackframe.h @@ -216,12 +216,19 @@ LONG_S $25, PT_R25(sp) LONG_S $28, PT_R28(sp) LONG_S $31, PT_R31(sp) + + /* Set thread_info if we're coming from user mode */ + mfc0 k0, CP0_STATUS + sll k0, 3 /* extract cu0 bit */ + bltz k0, 9f + ori $28, sp, _THREAD_MASK xori $28, _THREAD_MASK #ifdef CONFIG_CPU_CAVIUM_OCTEON .set mips64 pref 0, 0($28) /* Prefetch the current pointer */ #endif +9: .set pop .endm -- 2.7.4
