LU-8304 libcfs: convert debug_ctlwq to a completion.

kthread_run might sleep during an allocation, and so
it's considered unsafe to call with a state that's not
RUNNABLE.
Rather than move the state setting to after kthread_run, which
introduces a small race, replace the waitqueue with a completion.
This has clean semantics which perfectly match the need here.

Change-Id: Ic3bcf21dc747d73ce482e2d50bffd6c43fc04fbc
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-on: https://review.whamcloud.com/37398
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/libcfs/libcfs/debug.c b/libcfs/libcfs/debug.c
index 3cc732f..f48d9e5 100644 (file)
--- a/libcfs/libcfs/debug.c
+++ b/libcfs/libcfs/debug.c
@@ -249,7 +249,7 @@ MODULE_PARM_DESC(libcfs_panic_on_lbug, "Lustre kernel panic on LBUG");
 atomic_t libcfs_kmemory = ATOMIC_INIT(0);
 EXPORT_SYMBOL(libcfs_kmemory);
 
-static wait_queue_head_t debug_ctlwq;
+static DECLARE_COMPLETION(debug_complete);
 
 char libcfs_debug_file_path_arr[PATH_MAX] = LIBCFS_DEBUG_FILE_PATH_DEFAULT;
 EXPORT_SYMBOL(libcfs_debug_file_path_arr);
@@ -396,26 +396,22 @@ void libcfs_debug_dumplog_internal(void *arg)
 static int libcfs_debug_dumplog_thread(void *arg)
 {
        libcfs_debug_dumplog_internal(arg);
-       wake_up(&debug_ctlwq);
+       complete(&debug_complete);
        return 0;
 }
 
 void libcfs_debug_dumplog(void)
 {
-       wait_queue_entry_t wait;
        struct task_struct *dumper;
 
        ENTRY;
-
-       /*
-        * we're being careful to ensure that the kernel thread is
-        * able to set our state to running as it exits before we
-        * get to schedule()
+       /* If a previous call was interrupted, debug_complete->done
+        * might be elevated, and so we won't actually wait here.
+        * So we reinit the completion to ensure we wait for
+        * one thread to complete, though it might not be the one
+        * we start if there are overlaping thread.
         */
-       init_waitqueue_entry(&wait, current);
-       set_current_state(TASK_INTERRUPTIBLE);
-       add_wait_queue(&debug_ctlwq, &wait);
-
+       reinit_completion(&debug_complete);
        dumper = kthread_run(libcfs_debug_dumplog_thread,
                             (void *)(long)current_pid(),
                             "libcfs_debug_dumper");
@@ -423,11 +419,7 @@ void libcfs_debug_dumplog(void)
                pr_err("LustreError: cannot start log dump thread: rc = %ld\n",
                       PTR_ERR(dumper));
        else
-               schedule();
-
-       /* be sure to teardown if cfs_create_thread() failed */
-       remove_wait_queue(&debug_ctlwq, &wait);
-       set_current_state(TASK_RUNNING);
+               wait_for_completion_interruptible(&debug_complete);
 }
 EXPORT_SYMBOL(libcfs_debug_dumplog);
 
@@ -436,8 +428,6 @@ int libcfs_debug_init(unsigned long bufsize)
        int rc = 0;
        unsigned int max = libcfs_debug_mb;
 
-       init_waitqueue_head(&debug_ctlwq);
-
        if (libcfs_console_max_delay <= 0 || /* not set by user or */
            libcfs_console_min_delay <= 0 || /* set to invalid values */
            libcfs_console_min_delay >= libcfs_console_max_delay) {