[PATCH v2] tty: serial: jsm: allocate queue buffer at probe time

[Zheyu Ma <zheyuma97@gmail.com>]

In function 'neo_intr', the driver uses 'ch->ch_equeue' and
'ch->ch_reuque'. These two pointers are initialized in 'jsm_tty_open',
but the interrupt handler 'neo_intr' has been registered in the probe
progress. If 'jsm_tty_open' has not been called at this time, it will
cause null pointer dereference.

Once the driver registers the interrupt handler, the driver should be
ready to handle it.

Fix this by allocating the memory at probe time and not at open time.

This log reveals it:

[   50.934983] BUG: kernel NULL pointer dereference, address:
0000000000000000
[   50.938297] #PF: supervisor write access in kernel mode
[   50.940075] #PF: error_code(0x0002) - not-present page
[   50.940460] PGD 0 P4D 0
[   50.940654] Oops: 0002 [#1] PREEMPT SMP PTI
[   50.940967] CPU: 2 PID: 0 Comm: swapper/2 Not tainted
5.12.4-g70e7f0549188-dirty #97
[   50.941554] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
[   50.942419] RIP: 0010:memcpy_fromio+0x75/0xa0
[   50.942759] Code: e9 02 f3 a5 41 f6 c5 02 74 02 66 a5 41 f6 c5 01 74
01 a4 e8 5d 93 6b ff 5b 41 5c 41 5d 5d c3 e8 51 93 6b ff 4c 89 e7 48 89
de <a4> 49 89 fc 48 89 f3 49 83 ed 01 eb a4 e8 39 93 6b ff 4c 89 e7 48
[   50.944158] RSP: 0018:ffffc90000118df8 EFLAGS: 00010046
[   50.944559] RAX: ffff888100258000 RBX: ffffc90007f0030f
RCX: 0000000000000000
[   50.945114] RDX: 0000000000000000 RSI: ffffc90007f0030f
RDI: 0000000000000000
[   50.945652] RBP: ffffc90000118e10 R08: 0000000000000000
R09: 0000000000000000
[   50.946192] R10: 0000000000000000 R11: 0000000000000001
R12: 0000000000000000
[   50.946729] R13: 0000000000000001 R14: 0000000007f0021e
R15: 0000000000000000
[   50.947279] FS:  0000000000000000(0000) GS:ffff88817bc80000(0000)
knlGS:0000000000000000
[   50.947912] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   50.948346] CR2: 0000000000000000 CR3: 0000000107950000
CR4: 00000000000006e0
[   50.948892] DR0: 0000000000000000 DR1: 0000000000000000
DR2: 0000000000000000
[   50.949429] DR3: 0000000000000000 DR6: 00000000fffe0ff0
DR7: 0000000000000400
[   50.949950] Call Trace:
[   50.950138]  <IRQ>
[   50.950292]  neo_copy_data_from_uart_to_queue+0x2f7/0x4e0
[   50.950694]  neo_intr+0x253/0x7a0
[   50.950975]  __handle_irq_event_percpu+0x53/0x3e0
[   50.951352]  handle_irq_event_percpu+0x35/0x90
[   50.951706]  handle_irq_event+0x39/0x60
[   50.951999]  handle_fasteoi_irq+0xc2/0x1d0
[   50.952319]  __common_interrupt+0x7f/0x150
[   50.952638]  common_interrupt+0xb4/0xd0
[   50.952954]  </IRQ>
[   50.953136]  asm_common_interrupt+0x1e/0x40
[   50.969513] Kernel panic - not syncing: Fatal exception in interrupt
[   50.970151] Dumping ftrace buffer:
[   50.970420]    (ftrace buffer empty)
[   50.970693] Kernel Offset: disabled
[   50.970968] Rebooting in 1 seconds..

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
Changes in v2:
    - Allocate the memory at probe time, instead of simply checking whether it
    is a null pointer.
---
 drivers/tty/serial/jsm/jsm_tty.c | 64 +++++++++++++-------------------
 1 file changed, 26 insertions(+), 38 deletions(-)

diff --git a/drivers/tty/serial/jsm/jsm_tty.c b/drivers/tty/serial/jsm/jsm_tty.c
index 8e42a7682c63..1c77c982daaf 100644
--- a/drivers/tty/serial/jsm/jsm_tty.c
+++ b/drivers/tty/serial/jsm/jsm_tty.c
@@ -195,44 +195,6 @@ static int jsm_tty_open(struct uart_port *port)
 	/* Get board pointer from our array of majors we have allocated */
 	brd = channel->ch_bd;
 
-	/*
-	 * Allocate channel buffers for read/write/error.
-	 * Set flag, so we don't get trounced on.
-	 */
-	channel->ch_flags |= (CH_OPENING);
-
-	/* Drop locks, as malloc with GFP_KERNEL can sleep */
-
-	if (!channel->ch_rqueue) {
-		channel->ch_rqueue = kzalloc(RQUEUESIZE, GFP_KERNEL);
-		if (!channel->ch_rqueue) {
-			jsm_dbg(INIT, &channel->ch_bd->pci_dev,
-				"unable to allocate read queue buf\n");
-			return -ENOMEM;
-		}
-	}
-	if (!channel->ch_equeue) {
-		channel->ch_equeue = kzalloc(EQUEUESIZE, GFP_KERNEL);
-		if (!channel->ch_equeue) {
-			jsm_dbg(INIT, &channel->ch_bd->pci_dev,
-				"unable to allocate error queue buf\n");
-			return -ENOMEM;
-		}
-	}
-
-	channel->ch_flags &= ~(CH_OPENING);
-	/*
-	 * Initialize if neither terminal is open.
-	 */
-	jsm_dbg(OPEN, &channel->ch_bd->pci_dev,
-		"jsm_open: initializing channel in open...\n");
-
-	/*
-	 * Flush input queues.
-	 */
-	channel->ch_r_head = channel->ch_r_tail = 0;
-	channel->ch_e_head = channel->ch_e_tail = 0;
-
 	brd->bd_ops->flush_uart_write(channel);
 	brd->bd_ops->flush_uart_read(channel);
 
@@ -420,6 +382,32 @@ int jsm_tty_init(struct jsm_board *brd)
 		ch->ch_close_delay = 250;
 
 		init_waitqueue_head(&ch->ch_flags_wait);
+
+		/*
+		 * Allocate channel buffers for read/write/error.
+		 * Set flag, so we don't get trounced on.
+		 */
+		ch->ch_flags |= (CH_OPENING);
+
+		/* Drop locks, as malloc with GFP_KERNEL can sleep */
+
+		if (!ch->ch_rqueue) {
+			ch->ch_rqueue = kzalloc(RQUEUESIZE, GFP_KERNEL);
+			if (!ch->ch_rqueue)
+				return -ENOMEM;
+		}
+		if (!ch->ch_equeue) {
+			ch->ch_equeue = kzalloc(EQUEUESIZE, GFP_KERNEL);
+			if (!ch->ch_equeue)
+				return -ENOMEM;
+		}
+
+		ch->ch_flags &= ~(CH_OPENING);
+		/*
+		 * Flush input queues.
+		 */
+		ch->ch_r_head = ch->ch_r_tail = 0;
+		ch->ch_e_head = ch->ch_e_tail = 0;
 	}
 
 	jsm_dbg(INIT, &brd->pci_dev, "finish\n");
-- 
2.17.6