From: Juergen Gross jgross@suse.com
[ Upstream commit 8480ed9c2bbd56fc86524998e5f2e3e22f5038f6 ]
Today the Xen ballooning is done via delayed work in a workqueue. This might result in workqueue hangups being reported in case of large amounts of memory are being ballooned in one go (here 16GB):
BUG: workqueue lockup - pool cpus=6 node=0 flags=0x0 nice=0 stuck for 64s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 12: cpus=6 node=0 flags=0x0 nice=0 active=2/256 refcnt=3 in-flight: 229:balloon_process pending: cache_reap workqueue events_freezable_power_: flags=0x84 pwq 12: cpus=6 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 pending: disk_events_workfn workqueue mm_percpu_wq: flags=0x8 pwq 12: cpus=6 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 pending: vmstat_update pool 12: cpus=6 node=0 flags=0x0 nice=0 hung=64s workers=3 idle: 2222 43
This can easily be avoided by using a dedicated kernel thread for doing the ballooning work.
Reported-by: Jan Beulich jbeulich@suse.com Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Boris Ostrovsky boris.ostrovsky@oracle.com Link: https://lore.kernel.org/r/20210827123206.15429-1-jgross@suse.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/xen/balloon.c | 62 +++++++++++++++++++++++++++++++------------ 1 file changed, 45 insertions(+), 17 deletions(-)
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index ebb05517b6aa..2762d246991b 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -43,6 +43,8 @@ #include <linux/sched.h> #include <linux/cred.h> #include <linux/errno.h> +#include <linux/freezer.h> +#include <linux/kthread.h> #include <linux/mm.h> #include <linux/memblock.h> #include <linux/pagemap.h> @@ -117,7 +119,7 @@ static struct ctl_table xen_root[] = { #define EXTENT_ORDER (fls(XEN_PFN_PER_PAGE) - 1)
/* - * balloon_process() state: + * balloon_thread() state: * * BP_DONE: done or nothing to do, * BP_WAIT: wait to be rescheduled, @@ -132,6 +134,8 @@ enum bp_state { BP_ECANCELED };
+/* Main waiting point for xen-balloon thread. */ +static DECLARE_WAIT_QUEUE_HEAD(balloon_thread_wq);
static DEFINE_MUTEX(balloon_mutex);
@@ -146,10 +150,6 @@ static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)]; static LIST_HEAD(ballooned_pages); static DECLARE_WAIT_QUEUE_HEAD(balloon_wq);
-/* Main work function, always executed in process context. */ -static void balloon_process(struct work_struct *work); -static DECLARE_DELAYED_WORK(balloon_worker, balloon_process); - /* When ballooning out (allocating memory to return to Xen) we don't really want the kernel to try too hard since that can trigger the oom killer. */ #define GFP_BALLOON \ @@ -383,7 +383,7 @@ static void xen_online_page(struct page *page, unsigned int order) static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v) { if (val == MEM_ONLINE) - schedule_delayed_work(&balloon_worker, 0); + wake_up(&balloon_thread_wq);
return NOTIFY_OK; } @@ -508,18 +508,43 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) }
/* - * As this is a work item it is guaranteed to run as a single instance only. + * Stop waiting if either state is not BP_EAGAIN and ballooning action is + * needed, or if the credit has changed while state is BP_EAGAIN. + */ +static bool balloon_thread_cond(enum bp_state state, long credit) +{ + if (state != BP_EAGAIN) + credit = 0; + + return current_credit() != credit || kthread_should_stop(); +} + +/* + * As this is a kthread it is guaranteed to run as a single instance only. * We may of course race updates of the target counts (which are protected * by the balloon lock), or with changes to the Xen hard limit, but we will * recover from these in time. */ -static void balloon_process(struct work_struct *work) +static int balloon_thread(void *unused) { enum bp_state state = BP_DONE; long credit; + unsigned long timeout; + + set_freezable(); + for (;;) { + if (state == BP_EAGAIN) + timeout = balloon_stats.schedule_delay * HZ; + else + timeout = 3600 * HZ; + credit = current_credit();
+ wait_event_interruptible_timeout(balloon_thread_wq, + balloon_thread_cond(state, credit), timeout); + + if (kthread_should_stop()) + return 0;
- do { mutex_lock(&balloon_mutex);
credit = current_credit(); @@ -546,12 +571,7 @@ static void balloon_process(struct work_struct *work) mutex_unlock(&balloon_mutex);
cond_resched(); - - } while (credit && state == BP_DONE); - - /* Schedule more work if there is some still to be done. */ - if (state == BP_EAGAIN) - schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ); + } }
/* Resets the Xen limit, sets new target, and kicks off processing. */ @@ -559,7 +579,7 @@ void balloon_set_new_target(unsigned long target) { /* No need for lock. Not read-modify-write updates. */ balloon_stats.target_pages = target; - schedule_delayed_work(&balloon_worker, 0); + wake_up(&balloon_thread_wq); } EXPORT_SYMBOL_GPL(balloon_set_new_target);
@@ -664,7 +684,7 @@ void free_xenballooned_pages(int nr_pages, struct page **pages)
/* The balloon may be too large now. Shrink it if needed. */ if (current_credit()) - schedule_delayed_work(&balloon_worker, 0); + wake_up(&balloon_thread_wq);
mutex_unlock(&balloon_mutex); } @@ -696,6 +716,8 @@ static void __init balloon_add_region(unsigned long start_pfn,
static int __init balloon_init(void) { + struct task_struct *task; + if (!xen_domain()) return -ENODEV;
@@ -739,6 +761,12 @@ static int __init balloon_init(void) } #endif
+ task = kthread_run(balloon_thread, NULL, "xen-balloon"); + if (IS_ERR(task)) { + pr_err("xen-balloon thread could not be started, ballooning will not work!\n"); + return PTR_ERR(task); + } + /* Init the xen-balloon driver. */ xen_balloon_init();