user/sven/linux.git/kernel/task_work.c, branch v6.12.49

sched/core: Disable page allocation in task_tick_mm_cid()

2024-10-11T08:49:32Z

With KASAN and PREEMPT_RT enabled, calling task_work_add() in task_tick_mm_cid() may cause the following splat. [ 63.696416] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48 [ 63.696416] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 610, name: modprobe [ 63.696416] preempt_count: 10001, expected: 0 [ 63.696416] RCU nest depth: 1, expected: 1 This problem is caused by the following call trace. sched_tick() [ acquire rq->__lock ] -> task_tick_mm_cid() -> task_work_add() -> __kasan_record_aux_stack() -> kasan_save_stack() -> stack_depot_save_flags() -> alloc_pages_mpol_noprof() -> __alloc_pages_noprof() -> get_page_from_freelist() -> rmqueue() -> rmqueue_pcplist() -> __rmqueue_pcplist() -> rmqueue_bulk() -> rt_spin_lock() The rq lock is a raw_spinlock_t. We can't sleep while holding it. IOW, we can't call alloc_pages() in stack_depot_save_flags(). The task_tick_mm_cid() function with its task_work_add() call was introduced by commit 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") in v6.4 kernel. Fortunately, there is a kasan_record_aux_stack_noalloc() variant that calls stack_depot_save_flags() while not allowing it to allocate new pages. To allow task_tick_mm_cid() to use task_work without page allocation, a new TWAF_NO_ALLOC flag is added to enable calling kasan_record_aux_stack_noalloc() instead of kasan_record_aux_stack() if set. The task_tick_mm_cid() function is modified to add this new flag. The possible downside is the missing stack trace in a KASAN report due to new page allocation required when task_work_add_noallloc() is called which should be rare. Fixes: 223baf9d17f2 ("sched: Fix performance regression introduced by mm_cid") Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20241010014432.194742-1-longman@redhat.com

task_work: make TWA_NMI_CURRENT handling conditional on IRQ_WORK

2024-07-29T19:05:06Z

The TWA_NMI_CURRENT handling very much depends on IRQ_WORK, but that isn't universally enabled everywhere. Maybe the IRQ_WORK infrastructure should just be unconditional - x86 ends up indirectly enabling it through unconditionally enabling PERF_EVENTS, for example. But it also gets enabled by having SMP support, or even if you just have PRINTK enabled. But in the meantime TWA_NMI_CURRENT causes tons of build failures on various odd minimal configs. Which did show up in linux-next, but despite that nobody bothered to fix it or even inform me until -rc1 was out. Fixes: 466e4d801cd4 ("task_work: Add TWA_NMI_CURRENT as an additional notify mode") Reported-by: Naresh Kamboju Reported-by: kernelci.org bot Reported-by: Guenter Roeck Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Signed-off-by: Linus Torvalds

task_work: Add TWA_NMI_CURRENT as an additional notify mode.

2024-07-09T11:26:34Z

Adding task_work from NMI context requires the following: - The kasan_record_aux_stack() is not NMU safe and must be avoided. - Using TWA_RESUME is NMI safe. If the NMI occurs while the CPU is in userland then it will continue in userland and not invoke the `work' callback. Add TWA_NMI_CURRENT as an additional notify mode. In this mode skip kasan and use irq_work in hardirq-mode to for needed interrupt. Set TIF_NOTIFY_RESUME within the irq_work callback due to k[ac]san instrumentation in test_and_set_bit() which does not look NMI safe in case of a report. Suggested-by: Peter Zijlstra Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20240704170424.1466941-3-bigeasy@linutronix.de

task_work: Introduce task_work_cancel() again

2024-07-09T11:26:32Z

Re-introduce task_work_cancel(), this time to cancel an actual callback and not *any* callback pointing to a given function. This is going to be needed for perf events event freeing. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240621091601.18227-3-frederic@kernel.org

task_work: s/task_work_cancel()/task_work_cancel_func()/

2024-07-09T11:26:31Z

A proper task_work_cancel() API that actually cancels a callback and not *any* callback pointing to a given function is going to be needed for perf events event freeing. Do the appropriate rename to prepare for that. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240621091601.18227-2-frederic@kernel.org

task_work: add kerneldoc annotation for 'data' argument

2023-09-19T20:21:32Z

A previous commit changed the arguments to task_work_cancel_match(), but didn't document all of them. Link: https://lkml.kernel.org/r/93938bff-baa3-4091-85f5-784aae297a07@kernel.dk Fixes: c7aab1a7c52b ("task_work: add helper for more targeted task_work canceling") Signed-off-by: Jens Axboe Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202309120307.zis3yQGe-lkp@intel.com/ Acked-by: Oleg Nesterov Signed-off-by: Andrew Morton

task_work: use try_cmpxchg in task_work_add, task_work_cancel_match and task_work_run

2022-09-12T04:55:10Z

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in task_work_add, task_work_cancel_match and task_work_run. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. The patch avoids extra memory read in case cmpxchg fails. Link: https://lkml.kernel.org/r/20220823152632.4517-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak Signed-off-by: Andrew Morton

task_work: allow TWA_SIGNAL without a rescheduling IPI

2022-04-30T14:39:32Z

Some use cases don't always need an IPI when sending a TWA_SIGNAL notification. Add TWA_SIGNAL_NO_IPI, which is just like TWA_SIGNAL, except it doesn't send an IPI to the target task. It merely sets TIF_NOTIFY_SIGNAL and wakes up the task. This can be useful in avoiding a forceful transition to the kernel if the task is running in userspace. Depending on the task_work in question, it may be quite fine waiting for the next reschedule or kernel enter anyway, or the use case may even have other mechanisms for hinting to the task that a transition may be useful. This can drive more cooperative scheduling of task_work. Reviewed-by: Pavel Begunkov Link: https://lore.kernel.org/r/821f42b6-7d91-8074-8212-d34998097de4@kernel.dk Signed-off-by: Jens Axboe

resume_user_mode: Move to resume_user_mode.h

2022-03-10T22:51:50Z

Move set_notify_resume and tracehook_notify_resume into resume_user_mode.h. While doing that rename tracehook_notify_resume to resume_user_mode_work. Update all of the places that included tracehook.h for these functions to include resume_user_mode.h instead. Update all of the callers of tracehook_notify_resume to call resume_user_mode_work. Reviewed-by: Kees Cook Link: https://lkml.kernel.org/r/20220309162454.123006-12-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman"

task_work: Introduce task_work_pending

2022-03-10T19:39:04Z

Wrap the test of task->task_works in a helper function to make it clear what is being tested. All of the other readers of task->task_work use READ_ONCE and this is even necessary on current as other processes can update task->task_work. So for consistency I have added READ_ONCE into task_work_pending. Reviewed-by: Kees Cook Link: https://lkml.kernel.org/r/20220309162454.123006-7-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman"