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Subject[PATCH 3/3] livepatch: Cleanup message handling in klp_try_switch_task()
Date
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 <pmladek@suse.com>
---
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
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