[PATCH] tty: n_gsm: fix sleep-in-atomic-context bug in gsm_control_send

[Duoming Zhou]

The function gsm_dlci_t1() is a timer handler that runs in an
atomic context, but it calls "kzalloc(..., GFP_KERNEL)" that
may sleep. As a result, the sleep-in-atomic-context bug will
happen. The process is shown below:

gsm_dlci_t1()
 gsm_dlci_open()
  gsm_modem_update()
   gsm_modem_upd_via_msc()
    gsm_control_send()
     kzalloc(sizeof(.., GFP_KERNEL) //may sleep

This patch changes the gfp_t parameter of kzalloc() from GFP_KERNEL to
GFP_ATOMIC in order to mitigate the bug.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/tty/n_gsm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 01c112e2e21..2a0de70e0be 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1670,7 +1670,7 @@ static struct gsm_control *gsm_control_send(struct gsm_mux *gsm,
 		unsigned int command, u8 *data, int clen)
 {
 	struct gsm_control *ctrl = kzalloc(sizeof(struct gsm_control),
-						GFP_KERNEL);
+						GFP_ATOMIC);
 	unsigned long flags;
 	if (ctrl == NULL)
 		return NULL;
-- 
2.17.1