user/sven/linux.git/kernel/kthread.c, branch v4.19.159

kthread_worker: prevent queuing delayed work from timer_fn when it is being canceled

2020-11-10T11:35:58Z

commit 6993d0fdbee0eb38bfac350aa016f65ad11ed3b1 upstream. There is a small race window when a delayed work is being canceled and the work still might be queued from the timer_fn: CPU0 CPU1 kthread_cancel_delayed_work_sync() __kthread_cancel_work_sync() __kthread_cancel_work() work->canceling++; kthread_delayed_work_timer_fn() kthread_insert_work(); BUG: kthread_insert_work() should not get called when work->canceling is set. Signed-off-by: Zqiang Signed-off-by: Andrew Morton Reviewed-by: Petr Mladek Acked-by: Tejun Heo Cc: Link: https://lkml.kernel.org/r/20201014083030.16895-1-qiang.zhang@windriver.com Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

kthread: Do not preempt current task if it is going to call schedule()

2020-08-26T08:31:00Z

commit 26c7295be0c5e6da3fa45970e9748be983175b1b upstream. when we create a kthread with ktrhead_create_on_cpu(),the child thread entry is ktread.c:ktrhead() which will be preempted by the parent after call complete(done) while schedule() is not called yet,then the parent will call wait_task_inactive(child) but the child is still on the runqueue, so the parent will schedule_hrtimeout() for 1 jiffy,it will waste a lot of time,especially on startup. parent child ktrhead_create_on_cpu() wait_fo_completion(&done) -----> ktread.c:ktrhead() |----- complete(done);--wakeup and preempted by parent kthread_bind() <------------| |-> schedule();--dequeue here wait_task_inactive(child) | schedule_hrtimeout(1 jiffy) -| So we hope the child just wakeup parent but not preempted by parent, and the child is going to call schedule() soon,then the parent will not call schedule_hrtimeout(1 jiffy) as the child is already dequeue. The same issue for ktrhead_park()&&kthread_parkme(). This patch can save 120ms on rk312x startup with CONFIG_HZ=300. Signed-off-by: Liang Chen Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Steven Rostedt (VMware) Link: https://lkml.kernel.org/r/20200306070133.18335-2-cl@rock-chips.com Signed-off-by: Chanho Park Signed-off-by: Greg Kroah-Hartman

Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2018-08-13T18:25:07Z

Pull scheduler updates from Thomas Gleixner: - Cleanup and improvement of NUMA balancing - Refactoring and improvements to the PELT (Per Entity Load Tracking) code - Watchdog simplification and related cleanups - The usual pile of small incremental fixes and improvements * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (41 commits) watchdog: Reduce message verbosity stop_machine: Reflow cpu_stop_queue_two_works() sched/numa: Move task_numa_placement() closer to numa_migrate_preferred() sched/numa: Use group_weights to identify if migration degrades locality sched/numa: Update the scan period without holding the numa_group lock sched/numa: Remove numa_has_capacity() sched/numa: Modify migrate_swap() to accept additional parameters sched/numa: Remove unused task_capacity from 'struct numa_stats' sched/numa: Skip nodes that are at 'hoplimit' sched/debug: Reverse the order of printing faults sched/numa: Use task faults only if numa_group is not yet set up sched/numa: Set preferred_node based on best_cpu sched/numa: Simplify load_too_imbalanced() sched/numa: Evaluate move once per node sched/numa: Remove redundant field sched/debug: Show the sum wait time of a task group sched/fair: Remove #ifdefs from scale_rt_capacity() sched/core: Remove get_cpu() from sched_fork() sched/cpufreq: Clarify sugov_get_util() sched/sysctl: Remove unused sched_time_avg_ms sysctl ...

kthread, tracing: Don't expose half-written comm when creating kthreads

2018-07-26T13:59:33Z

There is a window for racing when printing directly to task->comm, allowing other threads to see a non-terminated string. The vsnprintf function fills the buffer, counts the truncated chars, then finally writes the \0 at the end. creator other vsnprintf: fill (not terminated) count the rest trace_sched_waking(p): ... memcpy(comm, p->comm, TASK_COMM_LEN) write \0 The consequences depend on how 'other' uses the string. In our case, it was copied into the tracing system's saved cmdlines, a buffer of adjacent TASK_COMM_LEN-byte buffers (note the 'n' where 0 should be): crash-arm64> x/1024s savedcmd->saved_cmdlines | grep 'evenk' 0xffffffd5b3818640: "irq/497-pwr_evenkworker/u16:12" ...and a strcpy out of there would cause stack corruption: [224761.522292] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: ffffff9bf9783c78 crash-arm64> kbt | grep 'comm\|trace_print_context' #6 0xffffff9bf9783c78 in trace_print_context+0x18c(+396) comm (char [16]) = "irq/497-pwr_even" crash-arm64> rd 0xffffffd4d0e17d14 8 ffffffd4d0e17d14: 2f71726900000000 5f7277702d373934 ....irq/497-pwr_ ffffffd4d0e17d24: 726f776b6e657665 3a3631752f72656b evenkworker/u16: ffffffd4d0e17d34: f9780248ff003231 cede60e0ffffff9b 12..H.x......`.. ffffffd4d0e17d44: cede60c8ffffffd4 00000fffffffffd4 .....`.......... The workaround in e09e28671 (use strlcpy in __trace_find_cmdline) was likely needed because of this same bug. Solved by vsnprintf:ing to a local buffer, then using set_task_comm(). This way, there won't be a window where comm is not terminated. Link: http://lkml.kernel.org/r/20180726071539.188015-1-snild@sony.com Cc: stable@vger.kernel.org Fixes: bc0c38d139ec7 ("ftrace: latency tracer infrastructure") Reviewed-by: Steven Rostedt (VMware) Signed-off-by: Snild Dolkow Signed-off-by: Steven Rostedt (VMware)

kthread: Simplify kthread_park() completion

2018-07-03T07:20:44Z

Oleg explains the reason we could hit park+park is that smpboot_update_cpumask_percpu_thread()'s for_each_cpu_and(cpu, &tmp, cpu_online_mask) smpboot_park_kthread(); turns into: for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask, (void)and) smpboot_park_kthread(); on UP, ignoring the mask. But since we just completely removed that function, this is no longer relevant. So revert commit: b1f5b378e126 ("kthread: Allow kthread_park() on a parked kthread") Suggested-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

kthread, sched/core: Fix kthread_parkme() (again...)

2018-07-03T07:17:30Z

Gaurav reports that commit: 85f1abe0019f ("kthread, sched/wait: Fix kthread_parkme() completion issue") isn't working for him. Because of the following race: > controller Thread CPUHP Thread > takedown_cpu > kthread_park > kthread_parkme > Set KTHREAD_SHOULD_PARK > smpboot_thread_fn > set Task interruptible > > > wake_up_process > if (!(p->state & state)) > goto out; > > Kthread_parkme > SET TASK_PARKED > schedule > raw_spin_lock(&rq->lock) > ttwu_remote > waiting for __task_rq_lock > context_switch > > finish_lock_switch > > > > Case TASK_PARKED > kthread_park_complete > > > SET Running Furthermore, Oleg noticed that the whole scheduler TASK_PARKED handling is buggered because the TASK_DEAD thing is done with preemption disabled, the current code can still complete early on preemption :/ So basically revert that earlier fix and go with a variant of the alternative mentioned in the commit. Promote TASK_PARKED to special state to avoid the store-store issue on task->state leading to the WARN in kthread_unpark() -> __kthread_bind(). But in addition, add wait_task_inactive() to kthread_park() to ensure the task really is PARKED when we return from kthread_park(). This avoids the whole kthread still gets migrated nonsense -- although it would be really good to get this done differently. Reported-by: Gaurav Kohli Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 85f1abe0019f ("kthread, sched/wait: Fix kthread_parkme() completion issue") Signed-off-by: Ingo Molnar

kthread: Allow kthread_park() on a parked kthread

2018-05-25T06:03:51Z

The following commit: 85f1abe0019f ("kthread, sched/wait: Fix kthread_parkme() completion issue") added a WARN() in the case where we call kthread_park() on an already parked thread, because the old code wasn't doing the right thing there and it wasn't at all clear that would happen. It turns out, this does in fact happen, so we have to deal with it. Instead of potentially returning early, also wait for the completion. This does however mean we have to use complete_all() and re-initialize the completion on re-use. Reported-by: LKP Tested-by: Meelis Roos Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: kernel test robot Cc: wfg@linux.intel.com Cc: Thomas Gleixner Fixes: 85f1abe0019f ("kthread, sched/wait: Fix kthread_parkme() completion issue") Link: http://lkml.kernel.org/r/20180504091142.GI12235@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar

kthread, sched/wait: Fix kthread_parkme() completion issue

2018-05-03T05:38:05Z

Even with the wait-loop fixed, there is a further issue with kthread_parkme(). Upon hotplug, when we do takedown_cpu(), smpboot_park_threads() can return before all those threads are in fact blocked, due to the placement of the complete() in __kthread_parkme(). When that happens, sched_cpu_dying() -> migrate_tasks() can end up migrating such a still runnable task onto another CPU. Normally the task will have hit schedule() and gone to sleep by the time we do kthread_unpark(), which will then do __kthread_bind() to re-bind the task to the correct CPU. However, when we loose the initial TASK_PARKED store to the concurrent wakeup issue described previously, do the complete(), get migrated, it is possible to either: - observe kthread_unpark()'s clearing of SHOULD_PARK and terminate the park and set TASK_RUNNING, or - __kthread_bind()'s wait_task_inactive() to observe the competing TASK_RUNNING store. Either way the WARN() in __kthread_bind() will trigger and fail to correctly set the CPU affinity. Fix this by only issuing the complete() when the kthread has scheduled out. This does away with all the icky 'still running' nonsense. The alternative is to promote TASK_PARKED to a special state, this guarantees wait_task_inactive() cannot observe a 'stale' TASK_RUNNING and we'll end up doing the right thing, but this preserves the whole icky business of potentially migating the still runnable thing. Reported-by: Gaurav Kohli Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

kthread, sched/wait: Fix kthread_parkme() wait-loop

2018-05-03T05:38:04Z

Gaurav reported a problem with __kthread_parkme() where a concurrent try_to_wake_up() could result in competing stores to ->state which, when the TASK_PARKED store got lost bad things would happen. The comment near set_current_state() actually mentions this competing store, but only mentions the case against TASK_RUNNING. This same store, with different timing, can happen against a subsequent !RUNNING store. This normally is not a problem, because as per that same comment, the !RUNNING state store is inside a condition based wait-loop: for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); if (!need_sleep) break; schedule(); } __set_current_state(TASK_RUNNING); If we loose the (first) TASK_UNINTERRUPTIBLE store to a previous (concurrent) wakeup, the schedule() will NO-OP and we'll go around the loop once more. The problem here is that the TASK_PARKED store is not inside the KTHREAD_SHOULD_PARK condition wait-loop. There is a genuine issue with sleeps that do not have a condition; this is addressed in a subsequent patch. Reported-by: Gaurav Kohli Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Oleg Nesterov Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

treewide: Remove TIMER_FUNC_TYPE and TIMER_DATA_TYPE casts

2017-11-22T00:35:54Z

With all callbacks converted, and the timer callback prototype switched over, the TIMER_FUNC_TYPE cast is no longer needed, so remove it. Conversion was done with the following scripts: perl -pi -e 's|$TIMER_FUNC_TYPE$||g' \ $(git grep TIMER_FUNC_TYPE | cut -d: -f1 | sort -u) perl -pi -e 's|$TIMER_DATA_TYPE$||g' \ $(git grep TIMER_DATA_TYPE | cut -d: -f1 | sort -u) The now unused macros are also dropped from include/linux/timer.h. Signed-off-by: Kees Cook