ath10k: perform crash dump collection in workqueue

Commit 25733c4e67 ("ath10k: pci: use mutex for diagnostic window CE
polling") introduced a regression where we try to sleep (grab a mutex)
in an atomic context:

[  233.602619] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:254
[  233.602626] in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
[  233.602636] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         5.1.0-rc2 #4
[  233.602642] Hardware name: Google Scarlet (DT)
[  233.602647] Call trace:
[  233.602663]  dump_backtrace+0x0/0x11c
[  233.602672]  show_stack+0x20/0x28
[  233.602681]  dump_stack+0x98/0xbc
[  233.602690]  ___might_sleep+0x154/0x16c
[  233.602696]  __might_sleep+0x78/0x88
[  233.602704]  mutex_lock+0x2c/0x5c
[  233.602717]  ath10k_pci_diag_read_mem+0x68/0x21c [ath10k_pci]
[  233.602725]  ath10k_pci_diag_read32+0x48/0x74 [ath10k_pci]
[  233.602733]  ath10k_pci_dump_registers+0x5c/0x16c [ath10k_pci]
[  233.602741]  ath10k_pci_fw_crashed_dump+0xb8/0x548 [ath10k_pci]
[  233.602749]  ath10k_pci_napi_poll+0x60/0x128 [ath10k_pci]
[  233.602757]  net_rx_action+0x140/0x388
[  233.602766]  __do_softirq+0x1b0/0x35c
[...]

ath10k_pci_fw_crashed_dump() is called from NAPI contexts, and firmware
memory dumps are retrieved using the diag memory interface.

A simple reproduction case is to run this on QCA6174A /
WLAN.RM.4.4.1-00132-QCARMSWP-1, which happens to be a way to b0rk the
firmware:

  dd if=/sys/kernel/debug/ieee80211/phy0/ath10k/mem_value bs=4K count=1
of=/dev/null

(NB: simulated firmware crashes, via debugfs, don't trigger firmware
dumps.)

The fix is to move the crash-dump into a workqueue context, and avoid
relying on 'data_lock' for most mutual exclusion. We only keep using it
here for protecting 'fw_crash_counter', while the rest of the coredump
buffers are protected by a new 'dump_mutex'.

I've tested the above with simulated firmware crashes (debugfs 'reset'
file), real firmware crashes (the 'dd' command above), and a variety of
reboot and suspend/resume configurations on QCA6174A.

Reported here:
http://lkml.kernel.org/linux-wireless/20190325202706.GA68720@google.com

Fixes: 25733c4e67 ("ath10k: pci: use mutex for diagnostic window CE polling")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath10k/ce.c

@@ -1855,7 +1855,7 @@ void ath10k_ce_dump_registers(struct ath10k *ar,
 	struct ath10k_ce_crash_data ce_data;
 	u32 addr, id;
 
-	lockdep_assert_held(&ar->data_lock);
+	lockdep_assert_held(&ar->dump_mutex);
 
 	ath10k_err(ar, "Copy Engine register dump:\n");
 

drivers/net/wireless/ath/ath10k/core.c

@@ -3119,6 +3119,7 @@ struct ath10k *ath10k_core_create(size_t priv_size, struct device *dev,
 		goto err_free_wq;
 
 	mutex_init(&ar->conf_mutex);
+	mutex_init(&ar->dump_mutex);
 	spin_lock_init(&ar->data_lock);
 
 	INIT_LIST_HEAD(&ar->peers);

drivers/net/wireless/ath/ath10k/core.h

@@ -1063,6 +1063,9 @@ struct ath10k {
 	/* prevents concurrent FW reconfiguration */
 	struct mutex conf_mutex;
 
+	/* protects coredump data */
+	struct mutex dump_mutex;
+
 	/* protects shared structure data */
 	spinlock_t data_lock;
 

drivers/net/wireless/ath/ath10k/coredump.c

@@ -1102,7 +1102,7 @@ struct ath10k_fw_crash_data *ath10k_coredump_new(struct ath10k *ar)
 {
 	struct ath10k_fw_crash_data *crash_data = ar->coredump.fw_crash_data;
 
-	lockdep_assert_held(&ar->data_lock);
+	lockdep_assert_held(&ar->dump_mutex);
 
 	if (ath10k_coredump_mask == 0)
 		/* coredump disabled */
@@ -1146,7 +1146,7 @@ static struct ath10k_dump_file_data *ath10k_coredump_build(struct ath10k *ar)
 	if (!buf)
 		return NULL;
 
-	spin_lock_bh(&ar->data_lock);
+	mutex_lock(&ar->dump_mutex);
 
 	dump_data = (struct ath10k_dump_file_data *)(buf);
 	strlcpy(dump_data->df_magic, "ATH10K-FW-DUMP",
@@ -1213,7 +1213,7 @@ static struct ath10k_dump_file_data *ath10k_coredump_build(struct ath10k *ar)
 		sofar += sizeof(*dump_tlv) + crash_data->ramdump_buf_len;
 	}
 
-	spin_unlock_bh(&ar->data_lock);
+	mutex_unlock(&ar->dump_mutex);
 
 	return dump_data;
 }

drivers/net/wireless/ath/ath10k/pci.c

@@ -1441,7 +1441,7 @@ static void ath10k_pci_dump_registers(struct ath10k *ar,
 	__le32 reg_dump_values[REG_DUMP_COUNT_QCA988X] = {};
 	int i, ret;
 
-	lockdep_assert_held(&ar->data_lock);
+	lockdep_assert_held(&ar->dump_mutex);
 
 	ret = ath10k_pci_diag_read_hi(ar, &reg_dump_values[0],
 				      hi_failure_state,
@@ -1656,7 +1656,7 @@ static void ath10k_pci_dump_memory(struct ath10k *ar,
 	int ret, i;
 	u8 *buf;
 
-	lockdep_assert_held(&ar->data_lock);
+	lockdep_assert_held(&ar->dump_mutex);
 
 	if (!crash_data)
 		return;
@@ -1734,14 +1734,19 @@ static void ath10k_pci_dump_memory(struct ath10k *ar,
 	}
 }
 
-static void ath10k_pci_fw_crashed_dump(struct ath10k *ar)
+static void ath10k_pci_fw_dump_work(struct work_struct *work)
 {
+	struct ath10k_pci *ar_pci = container_of(work, struct ath10k_pci,
+						 dump_work);
 	struct ath10k_fw_crash_data *crash_data;
+	struct ath10k *ar = ar_pci->ar;
 	char guid[UUID_STRING_LEN + 1];
 
-	spin_lock_bh(&ar->data_lock);
+	mutex_lock(&ar->dump_mutex);
 
+	spin_lock_bh(&ar->data_lock);
 	ar->stats.fw_crash_counter++;
+	spin_unlock_bh(&ar->data_lock);
 
 	crash_data = ath10k_coredump_new(ar);
 
@@ -1756,11 +1761,18 @@ static void ath10k_pci_fw_crashed_dump(struct ath10k *ar)
 	ath10k_ce_dump_registers(ar, crash_data);
 	ath10k_pci_dump_memory(ar, crash_data);
 
-	spin_unlock_bh(&ar->data_lock);
+	mutex_unlock(&ar->dump_mutex);
 
 	queue_work(ar->workqueue, &ar->restart_work);
 }
 
+static void ath10k_pci_fw_crashed_dump(struct ath10k *ar)
+{
+	struct ath10k_pci *ar_pci = ath10k_pci_priv(ar);
+
+	queue_work(ar->workqueue, &ar_pci->dump_work);
+}
+
 void ath10k_pci_hif_send_complete_check(struct ath10k *ar, u8 pipe,
 					int force)
 {
@@ -3442,6 +3454,8 @@ int ath10k_pci_setup_resource(struct ath10k *ar)
 	spin_lock_init(&ar_pci->ps_lock);
 	mutex_init(&ar_pci->ce_diag_mutex);
 
+	INIT_WORK(&ar_pci->dump_work, ath10k_pci_fw_dump_work);
+
 	timer_setup(&ar_pci->rx_post_retry, ath10k_pci_rx_replenish_retry, 0);
 
 	if (QCA_REV_6174(ar) || QCA_REV_9377(ar))

drivers/net/wireless/ath/ath10k/pci.h

@@ -121,6 +121,8 @@ struct ath10k_pci {
 	/* For protecting ce_diag */
 	struct mutex ce_diag_mutex;
 
+	struct work_struct dump_work;
+
 	struct ath10k_ce ce;
 	struct timer_list rx_post_retry;