[PATCH] mailbox: mailbox-test: Fix __might_sleep() warning in mbox_test_message_read()

[Junhui Liu]

The following warning was observed when calling mbox_test_message_read()
for the first time:

[   69.246375] do not call blocking ops when !TASK_RUNNING; state=1 set at [<(____ptrval____)>] mbox_test_message_read+0xba/0x23e
[   69.258608] WARNING: CPU: 0 PID: 62 at kernel/sched/core.c:8741 __might_sleep+0x62/0x66

This is triggered because simple_read_from_buffer() called in
mbox_test_message_read() may sleep. As a result, the kernel warns about
blocking operations when the task state is not TASK_RUNNING.

Fix this by ensuring __set_current_state(TASK_RUNNING) is called before
executing code paths that may sleep.

Fixes: d597580d3737 ("generic ...copy_..._user primitives")
Signed-off-by: Junhui Liu <junhui.liu at pigmoral.tech>
---
Full message:

/sys/kernel/debug/soc:mailbox-test # cat message
[   69.241175] ------------[ cut here ]------------
[   69.246375] do not call blocking ops when !TASK_RUNNING; state=1 set at [<(____ptrval____)>] mbox_test_message_read+0xba/0x23e
[   69.258608] WARNING: CPU: 0 PID: 62 at kernel/sched/core.c:8741 __might_sleep+0x62/0x66
[   69.258746] Modules linked in:
[   69.258781] CPU: 0 UID: 0 PID: 62 Comm: cat Not tainted 6.15.0-rc6-00349-gde4124a71fa8-dirty #2 NONE
[   69.258820] Hardware name: Milk-V Duo (DT)
[   69.258831] epc : __might_sleep+0x62/0x66
[   69.258866]  ra : __might_sleep+0x62/0x66
[   69.258892] epc : ffffffff8004e548 ra : ffffffff8004e548 sp : ffffffc60022bc40
[   69.258913]  gp : ffffffff81717250 tp : ffffffd6023b8c80 t0 : 6100000000000000
[   69.258931]  t1 : 0000000000000064 t2 : 616320746f6e206f s0 : ffffffc60022bc60
[   69.258950]  s1 : ffffffff812001b0 a0 : 0000000000000072 a1 : ffffffff81688a60
[   69.258970]  a2 : 0000000000000010 a3 : 00000000000000c1 a4 : 0000000000000000
[   69.258989]  a5 : 0000000000000000 a6 : ffffffff8172ba60 a7 : 0000000000000038
[   69.259012]  s2 : 00000000000000c0 s3 : ffffffd602275400 s4 : ffffffd60226d180
[   69.259032]  s5 : 0000000200000022 s6 : ffffffd602275610 s7 : ffffffd602275400
[   69.259054]  s8 : ffffffd602239640 s9 : 0000000000001000 s10: 0000000000000001
[   69.259074]  s11: ffffffd6022396d8 t3 : ffffffff8172ba6f t4 : ffffffff8172ba6f
[   69.259097]  t5 : ffffffff8172ba70 t6 : ffffffc60022ba58
[   69.259114] status: 0000000200000120 badaddr: 0000000000000000 cause: 0000000000000003
[   69.259139] [<ffffffff8004e548>] __might_sleep+0x62/0x66
[   69.259180] [<ffffffff801998da>] __might_fault+0x1c/0x24
[   69.259253] [<ffffffff80430824>] _copy_to_user+0x28/0x90
[   69.259295] [<ffffffff8022facc>] simple_read_from_buffer+0x48/0x72
[   69.259356] [<ffffffff807e8c20>] mbox_test_message_read+0x1da/0x23e
[   69.259396] [<ffffffff80367c32>] full_proxy_read+0x48/0x88
[   69.259477] [<ffffffff801fdea8>] vfs_read+0xb2/0x288
[   69.259508] [<ffffffff801fe896>] ksys_read+0x56/0xc0
[   69.259535] [<ffffffff801fe914>] __riscv_sys_read+0x14/0x1c
[   69.259563] [<ffffffff80a083f6>] do_trap_ecall_u+0x186/0x206
[   69.259622] [<ffffffff80a12be2>] handle_exception+0x146/0x152
[   69.259688] ---[ end trace 0000000000000000 ]---
---
 drivers/mailbox/mailbox-test.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/mailbox/mailbox-test.c b/drivers/mailbox/mailbox-test.c
index c9dd8c42c0cdf9e4ff96da012d7fbdcb4c6bc130..2540808d550d34a8d5af523043e59dce9a0e0e10 100644
--- a/drivers/mailbox/mailbox-test.c
+++ b/drivers/mailbox/mailbox-test.c
@@ -200,11 +200,13 @@ static ssize_t mbox_test_message_read(struct file *filp, char __user *userbuf,
 
 		if (filp->f_flags & O_NONBLOCK) {
 			ret = -EAGAIN;
+			__set_current_state(TASK_RUNNING);
 			goto waitq_err;
 		}
 
 		if (signal_pending(current)) {
 			ret = -ERESTARTSYS;
+			__set_current_state(TASK_RUNNING);
 			goto waitq_err;
 		}
 		schedule();
@@ -231,9 +233,9 @@ static ssize_t mbox_test_message_read(struct file *filp, char __user *userbuf,
 
 	spin_unlock_irqrestore(&tdev->lock, flags);
 
+	__set_current_state(TASK_RUNNING);
 	ret = simple_read_from_buffer(userbuf, count, ppos, touser, MBOX_HEXDUMP_MAX_LEN);
 waitq_err:
-	__set_current_state(TASK_RUNNING);
 	remove_wait_queue(&tdev->waitq, &wait);
 kfree_err:
 	kfree(touser);

---
base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21
change-id: 20250518-fix-mailbox-test-warn-81fd373303b8

Best regards,
-- 
Junhui Liu <junhui.liu at pigmoral.tech>