WARN_ON_ONCE() could not be called safely under rq lock because of console deadlock issues. Fortunately, simple printk_deferred() is enough because the warning is printed from a well defined location and context.
Also klp_try_switch_task() is called under klp_mutex. Therefore, the buffer for debug messages could be static. Signed-off-by: Petr Mladek <[email protected]> --- kernel/livepatch/transition.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c index 9c89ae8b337a..e8183d18227f 100644 --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -254,6 +254,7 @@ static int klp_check_stack_func(struct klp_func *func, static int klp_check_stack(struct task_struct *task, char *err_buf) { static unsigned long entries[MAX_STACK_ENTRIES]; + static int enosys_warned; struct stack_trace trace; struct klp_object *obj; struct klp_func *func; @@ -263,8 +264,16 @@ static int klp_check_stack(struct task_struct *task, char *err_buf) trace.nr_entries = 0; trace.max_entries = MAX_STACK_ENTRIES; trace.entries = entries; + ret = save_stack_trace_tsk_reliable(task, &trace); - WARN_ON_ONCE(ret == -ENOSYS); + if (ret == -ENOSYS) { + if (!enosys_warned) { + printk_deferred(KERN_WARNING "%s: save_stack_trace_tsk_reliable() not supported on this architecture.\n", + __func__); + enosys_warned = 1; + } + return ret; + } if (ret) { snprintf(err_buf, STACK_ERR_BUF_SIZE, "%s: %s:%d has an unreliable stack\n", @@ -297,11 +306,11 @@ static int klp_check_stack(struct task_struct *task, char *err_buf) */ static bool klp_try_switch_task(struct task_struct *task) { + static char err_buf[STACK_ERR_BUF_SIZE]; struct rq *rq; struct rq_flags flags; int ret; bool success = false; - char err_buf[STACK_ERR_BUF_SIZE]; err_buf[0] = '\0'; @@ -336,15 +345,15 @@ static bool klp_try_switch_task(struct task_struct *task) task_rq_unlock(rq, task, &flags); /* - * Due to console deadlock issues, pr_debug() can't be used while - * holding the task rq lock. Instead we have to use a temporary buffer + * printk_deferred() need to be used under rq lock to avoid + * console deadlock issues. But it does not support the dynamic + * debug feature. Instead we have to use a temporary buffer * and print the debug message after releasing the lock. */ if (err_buf[0] != '\0') pr_debug("%s", err_buf); return success; - } /* -- 2.16.4
