diff options
Diffstat (limited to 'debian/patches-rt/0324-tasklet-Address-a-race-resulting-in-double-enqueue.patch')
| -rw-r--r-- | debian/patches-rt/0324-tasklet-Address-a-race-resulting-in-double-enqueue.patch | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/debian/patches-rt/0324-tasklet-Address-a-race-resulting-in-double-enqueue.patch b/debian/patches-rt/0324-tasklet-Address-a-race-resulting-in-double-enqueue.patch new file mode 100644 index 000000000..70a6d70cb --- /dev/null +++ b/debian/patches-rt/0324-tasklet-Address-a-race-resulting-in-double-enqueue.patch @@ -0,0 +1,120 @@ +From f9bcdc9de0ced2b99b351e226344eb1c0246dd5c Mon Sep 17 00:00:00 2001 +From: Zhang Xiao <xiao.zhang@windriver.com> +Date: Tue, 17 Mar 2020 12:47:43 +0100 +Subject: [PATCH 324/347] tasklet: Address a race resulting in double-enqueue +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.246-rt110.tar.xz + +The kernel bugzilla has the following race condition reported: + +CPU0 CPU1 CPU2 +------------------------------------------------ +test_set SCHED + test_set RUN + if SCHED + add_list + raise + clear RUN +<softirq> +test_set RUN +test_clear SCHED + ->func + test_set SCHED +tasklet_try_unlock ->0 +test_clear SCHED + test_set SCHED + ->func +tasklet_try_unlock ->1 + test_set RUN + if SCHED + add list + raise + clear RUN + test_set RUN + if SCHED + add list + raise + clear RUN + +As a result the tasklet is enqueued on both CPUs and run on both CPUs. Due +to the nature of the list used here, it is possible that further +(different) tasklets, which are enqueued after this double-enqueued +tasklet, are scheduled on CPU2 but invoked on CPU1. It is also possible +that these tasklets won't be invoked at all, because during the second +enqueue process the t->next pointer is set to NULL - dropping everything +from the list. + +This race will trigger one or two of the WARN_ON() in +tasklet_action_common(). +The problem is that the tasklet may be invoked multiple times and clear +SCHED bit on each invocation. This makes it possible to enqueue the +very same tasklet on different CPUs. + +Current RT-devel is using the upstream implementation which does not +re-run tasklets if they have SCHED set again and so it does not clear +the SCHED bit multiple times on a single invocation. + +Introduce the CHAINED flag. The tasklet will only be enqueued if the +CHAINED flag has been set successfully. +If it is possible to exchange the flags (CHAINED | RUN) -> 0 then the +tasklet won't be re-run. Otherwise the possible SCHED flag is removed +and the tasklet is re-run again. + +Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=61451 +Not-signed-off-by: Zhang Xiao <xiao.zhang@windriver.com> +[bigeasy: patch description] +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> + +Signed-off-by: Tom Zanussi <zanussi@kernel.org> +--- + include/linux/interrupt.h | 5 ++++- + kernel/softirq.c | 6 +++++- + 2 files changed, 9 insertions(+), 2 deletions(-) + +diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h +index 97d9ba26915e..a3b5edb26bc5 100644 +--- a/include/linux/interrupt.h ++++ b/include/linux/interrupt.h +@@ -579,12 +579,15 @@ enum + { + TASKLET_STATE_SCHED, /* Tasklet is scheduled for execution */ + TASKLET_STATE_RUN, /* Tasklet is running (SMP only) */ +- TASKLET_STATE_PENDING /* Tasklet is pending */ ++ TASKLET_STATE_PENDING, /* Tasklet is pending */ ++ TASKLET_STATE_CHAINED /* Tasklet is chained */ + }; + + #define TASKLET_STATEF_SCHED (1 << TASKLET_STATE_SCHED) + #define TASKLET_STATEF_RUN (1 << TASKLET_STATE_RUN) + #define TASKLET_STATEF_PENDING (1 << TASKLET_STATE_PENDING) ++#define TASKLET_STATEF_CHAINED (1 << TASKLET_STATE_CHAINED) ++#define TASKLET_STATEF_RC (TASKLET_STATEF_RUN | TASKLET_STATEF_CHAINED) + + #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT_FULL) + static inline int tasklet_trylock(struct tasklet_struct *t) +diff --git a/kernel/softirq.c b/kernel/softirq.c +index 25bcf2f2714b..73dae64bfc9c 100644 +--- a/kernel/softirq.c ++++ b/kernel/softirq.c +@@ -947,6 +947,10 @@ static void __tasklet_schedule_common(struct tasklet_struct *t, + * is locked before adding it to the list. + */ + if (test_bit(TASKLET_STATE_SCHED, &t->state)) { ++ if (test_and_set_bit(TASKLET_STATE_CHAINED, &t->state)) { ++ tasklet_unlock(t); ++ return; ++ } + t->next = NULL; + *head->tail = t; + head->tail = &(t->next); +@@ -1040,7 +1044,7 @@ static void tasklet_action_common(struct softirq_action *a, + again: + t->func(t->data); + +- while (!tasklet_tryunlock(t)) { ++ while (cmpxchg(&t->state, TASKLET_STATEF_RC, 0) != TASKLET_STATEF_RC) { + /* + * If it got disabled meanwhile, bail out: + */ +-- +2.36.1 + |