user/sven/linux.git/kernel/rcu, branch v6.9.3

rcu: Fix buffer overflow in print_cpu_stall_info()

2024-05-30T07:44:06Z

[ Upstream commit 3758f7d9917bd7ef0482c4184c0ad673b4c4e069 ] The rcuc-starvation output from print_cpu_stall_info() might overflow the buffer if there is a huge difference in jiffies difference. The situation might seem improbable, but computers sometimes get very confused about time, which can result in full-sized integers, and, in this case, buffer overflow. Also, the unsigned jiffies difference is printed using %ld, which is normally for signed integers. This is intentional for debugging purposes, but it is not obvious from the code. This commit therefore changes sprintf() to snprintf() and adds a clarifying comment about intention of %ld format. Found by Linux Verification Center (linuxtesting.org) with SVACE. Fixes: 245a62982502 ("rcu: Dump rcuc kthread status for CPUs not reporting quiescent state") Signed-off-by: Nikita Kiryushin Reviewed-by: Steven Rostedt (Google) Signed-off-by: Paul E. McKenney Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Sasha Levin

rcu-tasks: Fix show_rcu_tasks_trace_gp_kthread buffer overflow

2024-05-30T07:44:05Z

[ Upstream commit cc5645fddb0ce28492b15520306d092730dffa48 ] There is a possibility of buffer overflow in show_rcu_tasks_trace_gp_kthread() if counters, passed to sprintf() are huge. Counter numbers, needed for this are unrealistically high, but buffer overflow is still possible. Use snprintf() with buffer size instead of sprintf(). Found by Linux Verification Center (linuxtesting.org) with SVACE. Fixes: edf3775f0ad6 ("rcu-tasks: Add count for idle tasks on offline CPUs") Signed-off-by: Nikita Kiryushin Reviewed-by: Steven Rostedt (Google) Signed-off-by: Paul E. McKenney Signed-off-by: Uladzislau Rezki (Sony) Signed-off-by: Sasha Levin

Merge branches 'rcu-doc.2024.02.14a', 'rcu-nocb.2024.02.14a', 'rcu-exp.2024.02.14a', 'rcu-tasks.2024.02.26a' and 'rcu-misc.2024.02.14a' into rcu.2024.02.26a

2024-02-27T01:37:25Z

rcu-tasks: Maintain real-time response in rcu_tasks_postscan()

2024-02-25T22:27:49Z

The current code will scan the entirety of each per-CPU list of exiting tasks in ->rtp_exit_list with interrupts disabled. This is normally just fine, because each CPU typically won't have very many tasks in this state. However, if a large number of tasks block late in do_exit(), these lists could be arbitrarily long. Low probability, perhaps, but it really could happen. This commit therefore occasionally re-enables interrupts while traversing these lists, inserting a dummy element to hold the current place in the list. In kernels built with CONFIG_PREEMPT_RT=y, this re-enabling happens after each list element is processed, otherwise every one-to-two jiffies. [ paulmck: Apply Frederic Weisbecker feedback. ] Link: https://lore.kernel.org/all/ZdeI_-RfdLR8jlsm@localhost.localdomain/ Signed-off-by: Paul E. McKenney Cc: Thomas Gleixner Cc: Sebastian Siewior Cc: Anna-Maria Behnsen Cc: Steven Rostedt Signed-off-by: Boqun Feng

rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks

2024-02-25T22:21:43Z

Holding a mutex across synchronize_rcu_tasks() and acquiring that same mutex in code called from do_exit() after its call to exit_tasks_rcu_start() but before its call to exit_tasks_rcu_stop() results in deadlock. This is by design, because tasks that are far enough into do_exit() are no longer present on the tasks list, making it a bit difficult for RCU Tasks to find them, let alone wait on them to do a voluntary context switch. However, such deadlocks are becoming more frequent. In addition, lockdep currently does not detect such deadlocks and they can be difficult to reproduce. In addition, if a task voluntarily context switches during that time (for example, if it blocks acquiring a mutex), then this task is in an RCU Tasks quiescent state. And with some adjustments, RCU Tasks could just as well take advantage of that fact. This commit therefore eliminates these deadlock by replacing the SRCU-based wait for do_exit() completion with per-CPU lists of tasks currently exiting. A given task will be on one of these per-CPU lists for the same period of time that this task would previously have been in the previous SRCU read-side critical section. These lists enable RCU Tasks to find the tasks that have already been removed from the tasks list, but that must nevertheless be waited upon. The RCU Tasks grace period gathers any of these do_exit() tasks that it must wait on, and adds them to the list of holdouts. Per-CPU locking and get_task_struct() are used to synchronize addition to and removal from these lists. Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/ Reported-by: Chen Zhongjin Reported-by: Yang Jihong Signed-off-by: Paul E. McKenney Tested-by: Yang Jihong Tested-by: Chen Zhongjin Reviewed-by: Frederic Weisbecker Signed-off-by: Boqun Feng

rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks

2024-02-25T22:21:43Z

This commit continues the elimination of deadlocks involving do_exit() and RCU tasks by causing exit_tasks_rcu_start() to add the current task to a per-CPU list and causing exit_tasks_rcu_stop() to remove the current task from whatever list it is on. These lists will be used to track tasks that are exiting, while still accounting for any RCU-tasks quiescent states that these tasks pass though. [ paulmck: Apply Frederic Weisbecker feedback. ] Link: https://lore.kernel.org/all/20240118021842.290665-1-chenzhongjin@huawei.com/ Reported-by: Chen Zhongjin Reported-by: Yang Jihong Signed-off-by: Paul E. McKenney Tested-by: Yang Jihong Tested-by: Chen Zhongjin Reviewed-by: Frederic Weisbecker Signed-off-by: Boqun Feng

rcu-tasks: Initialize data to eliminate RCU-tasks/do_exit() deadlocks

2024-02-25T22:21:43Z

rcu-tasks: Initialize callback lists at rcu_init() time

2024-02-25T22:21:34Z

In order for RCU Tasks to reliably maintain per-CPU lists of exiting tasks, those lists must be initialized before it is possible for tasks to exit, especially given that the boot CPU is not necessarily CPU 0 (an example being, powerpc kexec() kernels). And at the time that rcu_init_tasks_generic() is called, a task could potentially exit, unconventional though that sort of thing might be. This commit therefore moves the calls to cblist_init_generic() from functions called from rcu_init_tasks_generic() to a new function named tasks_cblist_init_generic() that is invoked from rcu_init(). This constituted a bug in a commit that never went to mainline, so there is no need for any backporting to -stable. Reported-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng

rcu-tasks: Add data to eliminate RCU-tasks/do_exit() deadlocks

2024-02-25T22:18:24Z

rcu/sync: remove un-used rcu_sync_enter_start function

2024-02-14T16:00:57Z

With commit '6a010a49b63a ("cgroup: Make !percpu threadgroup_rwsem operations optional")' usage of rcu_sync_enter_start is removed. So this function can also be removed. In the words of Oleg Nesterov: __rcu_sync_enter(wait => false) is a better alternative if someone needs rcu_sync_enter_start() again. Link: https://lore.kernel.org/all/20220725121208.GB28662@redhat.com/ Signed-off-by: Onkarnath Signed-off-by: Maninder Singh Acked-by: Oleg Nesterov Acked-by: Tejun Heo Reviewed-by: Paul E. McKenney Signed-off-by: Boqun Feng