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, 99 insertions, 0 deletions

diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
new file mode 100644
index 000000000..fe6599800
--- /dev/null
+++ b/tools/memory-model/linux-kernel.bell
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0+
+(*
+ * Copyright (C) 2015 Jade Alglave <j.alglave@ucl.ac.uk>,
+ * Copyright (C) 2016 Luc Maranget <luc.maranget@inria.fr> for Inria
+ * Copyright (C) 2017 Alan Stern <stern@rowland.harvard.edu>,
+ *                    Andrea Parri <parri.andrea@gmail.com>
+ *
+ * An earlier version of this file appeared in the companion webpage for
+ * "Frightening small children and disconcerting grown-ups: Concurrency
+ * in the Linux kernel" by Alglave, Maranget, McKenney, Parri, and Stern,
+ * which appeared in ASPLOS 2018.
+ *)
+
+"Linux-kernel memory consistency model"
+
+enum Accesses = 'ONCE (*READ_ONCE,WRITE_ONCE*) ||
+		'RELEASE (*smp_store_release*) ||
+		'ACQUIRE (*smp_load_acquire*) ||
+		'NORETURN (* R of non-return RMW *) ||
+		'MB (*xchg(),cmpxchg(),...*)
+instructions R[Accesses]
+instructions W[Accesses]
+instructions RMW[Accesses]
+
+enum Barriers = 'wmb (*smp_wmb*) ||
+		'rmb (*smp_rmb*) ||
+		'MB (*smp_mb*) ||
+		'barrier (*barrier*) ||
+		'rcu-lock (*rcu_read_lock*)  ||
+		'rcu-unlock (*rcu_read_unlock*) ||
+		'sync-rcu (*synchronize_rcu*) ||
+		'before-atomic (*smp_mb__before_atomic*) ||
+		'after-atomic (*smp_mb__after_atomic*) ||
+		'after-spinlock (*smp_mb__after_spinlock*) ||
+		'after-unlock-lock (*smp_mb__after_unlock_lock*) ||
+		'after-srcu-read-unlock (*smp_mb__after_srcu_read_unlock*)
+instructions F[Barriers]
+
+
+(*
+ * Filter out syntactic annotations that do not provide the corresponding
+ * semantic ordering, such as Acquire on a store or Mb on a failed RMW.
+ *)
+let FailedRMW = RMW \ (domain(rmw) | range(rmw))
+let Acquire = ACQUIRE \ W \ FailedRMW
+let Release = RELEASE \ R \ FailedRMW
+let Mb = MB \ FailedRMW
+let Noreturn = NORETURN \ W
+
+(* SRCU *)
+enum SRCU = 'srcu-lock || 'srcu-unlock || 'sync-srcu
+instructions SRCU[SRCU]
+(* All srcu events *)
+let Srcu = Srcu-lock | Srcu-unlock | Sync-srcu
+
+(* Compute matching pairs of nested Rcu-lock and Rcu-unlock *)
+let rcu-rscs = let rec
+	    unmatched-locks = Rcu-lock \ domain(matched)
+	and unmatched-unlocks = Rcu-unlock \ range(matched)
+	and unmatched = unmatched-locks | unmatched-unlocks
+	and unmatched-po = [unmatched] ; po ; [unmatched]
+	and unmatched-locks-to-unlocks =
+		[unmatched-locks] ; po ; [unmatched-unlocks]
+	and matched = matched | (unmatched-locks-to-unlocks \
+		(unmatched-po ; unmatched-po))
+	in matched
+
+(* Validate nesting *)
+flag ~empty Rcu-lock \ domain(rcu-rscs) as unmatched-rcu-lock
+flag ~empty Rcu-unlock \ range(rcu-rscs) as unmatched-rcu-unlock
+
+(* Compute matching pairs of nested Srcu-lock and Srcu-unlock *)
+let carry-srcu-data = (data ; [~ Srcu-unlock] ; rf)*
+let srcu-rscs = ([Srcu-lock] ; carry-srcu-data ; data ; [Srcu-unlock]) & loc
+
+(* Validate nesting *)
+flag ~empty Srcu-lock \ domain(srcu-rscs) as unmatched-srcu-lock
+flag ~empty Srcu-unlock \ range(srcu-rscs) as unmatched-srcu-unlock
+flag ~empty (srcu-rscs^-1 ; srcu-rscs) \ id as multiple-srcu-matches
+
+(* Check for use of synchronize_srcu() inside an RCU critical section *)
+flag ~empty rcu-rscs & (po ; [Sync-srcu] ; po) as invalid-sleep
+
+(* Validate SRCU dynamic match *)
+flag ~empty different-values(srcu-rscs) as srcu-bad-value-match
+
+(* Compute marked and plain memory accesses *)
+let Marked = (~M) | IW | ONCE | RELEASE | ACQUIRE | MB | RMW |
+		LKR | LKW | UL | LF | RL | RU | Srcu-lock | Srcu-unlock
+let Plain = M \ Marked
+
+(* Redefine dependencies to include those carried through plain accesses *)
+let carry-dep = (data ; [~ Srcu-unlock] ; rfi)*
+let addr = carry-dep ; addr
+let ctrl = carry-dep ; ctrl
+let data = carry-dep ; data
+
+flag ~empty (if "lkmmv2" then 0 else _)
+  as this-model-requires-variant-higher-than-lkmmv1