diff options
| author | Sami Tolvanen <samitolvanen@google.com> | 2020-06-01 12:20:04 -0700 |
|---|---|---|
| committer | Sami Tolvanen <samitolvanen@google.com> | 2020-06-02 17:37:03 +0000 |
| commit | c0ff3cd9d7d5e2f51c0b691128800b0b0cf7da2c (patch) | |
| tree | 3f1bc723cf7e3c3b73f242492b9150e470617ed5 | |
| parent | 7b8513eb008b7ed331af838edc3344d172a94ac0 (diff) | |
ANDROID: scs: fix recursive spinlock in scs_check_usage
Use cmpxchg instead of a spinlock in scs_check_usage() to avoid
deadlocks.
Bug: 157781894
Change-Id: I1701ccaf25fdbd34ce4798c6f93e220b1565fb34
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
| -rw-r--r-- | kernel/scs.c | 39 |
1 files changed, 17 insertions, 22 deletions
diff --git a/kernel/scs.c b/kernel/scs.c index ad74d13f2c0f..c8e53358e20a 100644 --- a/kernel/scs.c +++ b/kernel/scs.c @@ -185,36 +185,31 @@ int scs_prepare(struct task_struct *tsk, int node) } #ifdef CONFIG_DEBUG_STACK_USAGE -static inline unsigned long scs_used(struct task_struct *tsk) +static void scs_check_usage(struct task_struct *tsk) { + static unsigned long highest; + unsigned long *p = __scs_base(tsk); unsigned long *end = scs_magic(p); - unsigned long s = (unsigned long)p; - - while (p < end && READ_ONCE_NOCHECK(*p)) - p++; + unsigned long prev, curr = highest, used = 0; - return (unsigned long)p - s; -} - -static void scs_check_usage(struct task_struct *tsk) -{ - static DEFINE_SPINLOCK(lock); - static unsigned long highest; - unsigned long used = scs_used(tsk); + for (; p < end; ++p) { + if (!READ_ONCE_NOCHECK(*p)) + break; + used += sizeof(*p); + } - if (used <= highest) - return; + while (used > curr) { + prev = cmpxchg_relaxed(&highest, curr, used); - spin_lock(&lock); + if (prev == curr) { + pr_info("%s (%d): highest shadow stack usage: %lu bytes\n", + tsk->comm, task_pid_nr(tsk), used); + break; + } - if (used > highest) { - pr_info("%s (%d): highest shadow stack usage: %lu bytes\n", - tsk->comm, task_pid_nr(tsk), used); - highest = used; + curr = prev; } - - spin_unlock(&lock); } #else static inline void scs_check_usage(struct task_struct *tsk) |