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Subject[PATCH] riscv: stacktrace: fix dump_backtrace/walk_stackframe with NULL task
Date
Some places try to show backtrace with NULL task, and expect the task is
'current'. For example, dump_stack()->show_stack(NULL,...). So the
stacktrace code should take care of this case.

Here is an oops caused by this issue when accessing the NULL task.

[ 15.180813] Kernel panic - not syncing: No working init found. Try passing init= option to kernel. See Linux Documentation/admin-guide/init.rst for guidance.
[ 15.182382] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc7-00111-g625acffd7ae2-dirty #18
[ 15.183431] Hardware name: riscv-virtio,qemu (DT)
[ 15.184253] Call Trace:
[ 15.223617] Unable to handle kernel paging request at virtual address 0000000000001590
[ 15.267378] Oops [#1]
[ 15.268215] Modules linked in:
[ 15.272027] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc7-00111-g625acffd7ae2-dirty #18
[ 15.273997] Hardware name: riscv-virtio,qemu (DT)
[ 15.275134] epc : walk_stackframe+0xc4/0xdc
[ 15.280146] ra : dump_backtrace+0x30/0x38
[ 15.280799] epc : ffffffff8000597e ra : ffffffff800059c6 sp : ffffffe002383d60
[ 15.281622] gp : ffffffff8179ad18 tp : ffffffe002378000 t0 : ffffffff81bc1a3f
[ 15.282574] t1 : 0000000000000001 t2 : 0000000000000000 s0 : ffffffe002383dc0
[ 15.283782] s1 : ffffffff812b7d18 a0 : 0000000000001000 a1 : 0000000000000000
[ 15.285115] a2 : ffffffff807ec668 a3 : ffffffff812b7d18 a4 : c76c00cabf08b500
[ 15.286213] a5 : 0000000000001000 a6 : 000000001a9ef260 a7 : 0000000000000000
[ 15.287317] s2 : 0000000000000000 s3 : 0000000000000000 s4 : 0000000000000000
[ 15.288323] s5 : ffffffff807ec668 s6 : ffffffff812b7d18 s7 : 0000000000000000
[ 15.289530] s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000000000000000
[ 15.290995] s11: 0000000000000000 t3 : 0000000000000001 t4 : 0000000000000000
[ 15.292465] t5 : 206f74206e6f6974 t6 : ffffffe002383b28
[ 15.293859] status: 0000000000000100 badaddr: 0000000000001590 cause: 000000000000000d
[ 15.296035] [<ffffffff8000597e>] walk_stackframe+0xc4/0xdc
[ 15.297342] [<ffffffff800059c6>] dump_backtrace+0x30/0x38
[ 15.298333] [<ffffffff807ec6e0>] show_stack+0x40/0x4c
[ 15.299765] [<ffffffff807f07ac>] dump_stack+0x7c/0x96
[ 15.300553] [<ffffffff807ec8be>] panic+0x118/0x300
[ 15.301147] [<ffffffff807f61e8>] kernel_init+0x12c/0x138
[ 15.302056] [<ffffffff80003a22>] ret_from_exception+0x0/0xc
[ 15.338628] ---[ end trace 0a3fa0cc7f3393cd ]---
[ 15.339919] note: swapper/0[1] exited with preempt_count 1
[ 15.341995] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[ 15.343889] SMP: stopping secondary CPUs
[ 16.802836] SMP: failed to stop secondary CPUs 0-3
[ 16.806264] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---

This patch fixes it by setting the task to current if it's NULL before
accessing it.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Fixes: 5d8544e2d0 ("RISC-V: Generic library routines and assembly")
---
arch/riscv/kernel/stacktrace.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index bde85fc53357..788b65eba965 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -23,6 +23,9 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
{
unsigned long fp, sp, pc;

+ if (!task)
+ task = current;
+
if (regs) {
fp = frame_pointer(regs);
sp = user_stack_pointer(regs);
@@ -73,6 +76,9 @@ void notrace walk_stackframe(struct task_struct *task,
unsigned long sp, pc;
unsigned long *ksp;

+ if (!task)
+ task = current;
+
if (regs) {
sp = user_stack_pointer(regs);
pc = instruction_pointer(regs);
--
2.30.2
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