user/sven/linux.git/kernel/rcu/refscale.c, branch v6.1.162

refscale: Fix uninitalized use of wait_queue_head_t

2023-09-13T07:42:28Z

[ Upstream commit f5063e8948dad7f31adb007284a5d5038ae31bb8 ] Running the refscale test occasionally crashes the kernel with the following error: [ 8569.952896] BUG: unable to handle page fault for address: ffffffffffffffe8 [ 8569.952900] #PF: supervisor read access in kernel mode [ 8569.952902] #PF: error_code(0x0000) - not-present page [ 8569.952904] PGD c4b048067 P4D c4b049067 PUD c4b04b067 PMD 0 [ 8569.952910] Oops: 0000 [#1] PREEMPT_RT SMP NOPTI [ 8569.952916] Hardware name: Dell Inc. PowerEdge R750/0WMWCR, BIOS 1.2.4 05/28/2021 [ 8569.952917] RIP: 0010:prepare_to_wait_event+0x101/0x190 : [ 8569.952940] Call Trace: [ 8569.952941] [ 8569.952944] ref_scale_reader+0x380/0x4a0 [refscale] [ 8569.952959] kthread+0x10e/0x130 [ 8569.952966] ret_from_fork+0x1f/0x30 [ 8569.952973] The likely cause is that init_waitqueue_head() is called after the call to the torture_create_kthread() function that creates the ref_scale_reader kthread. Although this init_waitqueue_head() call will very likely complete before this kthread is created and starts running, it is possible that the calling kthread will be delayed between the calls to torture_create_kthread() and init_waitqueue_head(). In this case, the new kthread will use the waitqueue head before it is properly initialized, which is not good for the kernel's health and well-being. The above crash happened here: static inline void __add_wait_queue(...) { : if (!(wq->flags & WQ_FLAG_PRIORITY)) <=== Crash here The offset of flags from list_head entry in wait_queue_entry is -0x18. If reader_tasks[i].wq.head.next is NULL as allocated reader_task structure is zero initialized, the instruction will try to access address 0xffffffffffffffe8, which is exactly the fault address listed above. This commit therefore invokes init_waitqueue_head() before creating the kthread. Fixes: 653ed64b01dc ("refperf: Add a test to measure performance of read-side synchronization") Signed-off-by: Waiman Long Reviewed-by: Qiuxu Zhuo Reviewed-by: Davidlohr Bueso Acked-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin

refscale: Move shutdown from wait_event() to wait_event_idle()

2023-05-24T16:32:33Z

[ Upstream commit 6bc6e6b27524304aadb9c04611ddb1c84dd7617a ] The ref_scale_shutdown() kthread/function uses wait_event() to wait for the refscale test to complete. However, although the read-side tests are normally extremely fast, there is no law against specifying a very large value for the refscale.loops module parameter or against having a slow read-side primitive. Either way, this might well trigger the hung-task timeout. This commit therefore replaces those wait_event() calls with calls to wait_event_idle(), which do not trigger the hung-task timeout. Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng Signed-off-by: Sasha Levin

refscale: Convert test_lock spinlock to raw_spinlock

2022-06-21T22:57:04Z

In kernels built with CONFIG_PREEMPT_RT=y, spinlocks are replaced by rt_mutex, which can sleep. This means that acquiring a non-raw spinlock in a critical section where preemption is disabled can trigger the following BUG: BUG: scheduling while atomic: ref_scale_reade/76/0x00000002 Preemption disabled at: ref_lock_section+0x16/0x80 Call Trace: dump_stack_lvl+0x5b/0x82 dump_stack+0x10/0x12 __schedule_bug.cold+0x9c/0xad __schedule+0x839/0xc00 schedule_rtlock+0x22/0x40 rtlock_slowlock_locked+0x460/0x1350 rt_spin_lock+0x61/0xe0 ref_lock_section+0x29/0x80 rcu_scale_one_reader+0x52/0x60 ref_scale_reader+0x28d/0x490 kthread+0x128/0x150 ret_from_fork+0x22/0x30 This commit therefore converts spinlock to raw_spinlock. Signed-off-by: Zqiang Signed-off-by: Paul E. McKenney

refscale: Allow refscale without RCU Tasks Rude/Trace

2022-04-20T23:53:19Z

Currently, a CONFIG_PREEMPT_NONE=y kernel substitutes normal RCU for RCU Tasks Rude and RCU Tasks Trace. Unless that kernel builds refscale, whether built-in or as a module, in which case these RCU Tasks flavors are (unnecessarily) built in. This both increases kernel size and increases the complexity of certain tracing operations. This commit therefore decouples the presence of refscale from the presence of RCU Tasks Rude and RCU Tasks Trace. Signed-off-by: Paul E. McKenney

refscale: Allow refscale without RCU Tasks

2022-04-20T23:53:19Z

Currently, a CONFIG_PREEMPT_NONE=y kernel substitutes normal RCU for RCU Tasks. Unless that kernel builds refscale, whether built-in or as a module, in which case RCU Tasks is (unnecessarily) built in. This both increases kernel size and increases the complexity of certain tracing operations. This commit therefore decouples the presence of refscale from the presence of RCU Tasks. Signed-off-by: Paul E. McKenney

refscale: Add missing '\n' to flush message

2021-12-08T00:36:12Z

Add '\n' to macros to flush message for each call. Acked-by: Davidlohr Bueso Signed-off-by: Li Zhijian Signed-off-by: Paul E. McKenney

refscale: Always log the error message

2021-12-08T00:31:44Z

An OOM is a serious error that should be logged even in non-verbose runs. This commit therefore adds an unconditional SCALEOUT_ERRSTRING() macro and uses it instead of VERBOSE_SCALEOUT_ERRSTRING() when reporting an OOM. [ paulmck: Drop do-while from SCALEOUT_ERRSTRING() due to only single statement. ] Signed-off-by: Li Zhijian Signed-off-by: Paul E. McKenney

refscale: Prevent buffer to pr_alert() being too long

2021-12-01T01:29:50Z

0Day/LKP observed that the refscale results fail to complete when larger values of nrun (such as 300) are specified. The problem is that printk() can accept at most a 1024-byte buffer. This commit therefore prints the buffer whenever its length exceeds 800 bytes. CC: Philip Li Reported-by: kernel test robot Signed-off-by: Li Zhijian Signed-off-by: Paul E. McKenney

refscale: Simplify the errexit checkpoint

2021-12-01T01:29:50Z

There is only the one OOM error case in main_func(), so this commit eliminates the errexit local variable in favor of a branch to cleanup code. Signed-off-by: Li Zhijian Signed-off-by: Paul E. McKenney

refscale: Warn on individual ref_scale_init() error conditions

2021-09-13T23:36:16Z

When running refscale as a module, any ref_scale_init() issues will be reflected in the error code from modprobe or insmod, as the case may be. However, these error codes are not available when running refscale built-in, for example, when using the kvm.sh script. This commit therefore adds WARN_ON_ONCE() to allow distinguishing ref_scale_init() errors when running refscale built-in. Signed-off-by: Paul E. McKenney