thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 73 insertions, 0 deletions

diff --git a/include/clocksource/timer-xilinx.h b/include/clocksource/timer-xilinx.h
new file mode 100644
index 000000000..d116f18de
--- /dev/null
+++ b/include/clocksource/timer-xilinx.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2021 Sean Anderson <sean.anderson@seco.com>
+ */
+
+#ifndef XILINX_TIMER_H
+#define XILINX_TIMER_H
+
+#include <linux/compiler.h>
+
+#define TCSR0	0x00
+#define TLR0	0x04
+#define TCR0	0x08
+#define TCSR1	0x10
+#define TLR1	0x14
+#define TCR1	0x18
+
+#define TCSR_MDT	BIT(0)
+#define TCSR_UDT	BIT(1)
+#define TCSR_GENT	BIT(2)
+#define TCSR_CAPT	BIT(3)
+#define TCSR_ARHT	BIT(4)
+#define TCSR_LOAD	BIT(5)
+#define TCSR_ENIT	BIT(6)
+#define TCSR_ENT	BIT(7)
+#define TCSR_TINT	BIT(8)
+#define TCSR_PWMA	BIT(9)
+#define TCSR_ENALL	BIT(10)
+#define TCSR_CASC	BIT(11)
+
+struct clk;
+struct device_node;
+struct regmap;
+
+/**
+ * struct xilinx_timer_priv - Private data for Xilinx AXI timer drivers
+ * @map: Regmap of the device, possibly with an offset
+ * @clk: Parent clock
+ * @max: Maximum value of the counters
+ */
+struct xilinx_timer_priv {
+	struct regmap *map;
+	struct clk *clk;
+	u64 max;
+};
+
+/**
+ * xilinx_timer_tlr_cycles() - Calculate the TLR for a period specified
+ *                             in clock cycles
+ * @priv: The timer's private data
+ * @tcsr: The value of the TCSR register for this counter
+ * @cycles: The number of cycles in this period
+ *
+ * Callers of this function MUST ensure that @cycles is representable as
+ * a TLR.
+ *
+ * Return: The calculated value for TLR
+ */
+u32 xilinx_timer_tlr_cycles(struct xilinx_timer_priv *priv, u32 tcsr,
+			    u64 cycles);
+
+/**
+ * xilinx_timer_get_period() - Get the current period of a counter
+ * @priv: The timer's private data
+ * @tlr: The value of TLR for this counter
+ * @tcsr: The value of TCSR for this counter
+ *
+ * Return: The period, in ns
+ */
+unsigned int xilinx_timer_get_period(struct xilinx_timer_priv *priv,
+				     u32 tlr, u32 tcsr);
+
+#endif /* XILINX_TIMER_H */