On 7/7/23 03:27, Zhuo, Qiuxu wrote:
From: Waiman Long <longman@xxxxxxxxxx> ... Subject: [PATCH] refscale: Fix use of uninitalized wait_queue_head_t It was found that running the refscale test might sometimes crash 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] <TASK> [ 8569.952944] ref_scale_reader+0x380/0x4a0 [refscale] [ 8569.952959] kthread+0x10e/0x130 [ 8569.952966] ret_from_fork+0x1f/0x30 [ 8569.952973] </TASK> This is likely caused by the fact that init_waitqueue_head() is called after the ref_scale_reader kthread is created. So the kthread may try to use the waitqueue head before it is properly initialized. Fix this by initializing the waitqueue head first before kthread creation. Fixes: 653ed64b01dc ("refperf: Add a test to measure performance of read- side synchronization") Signed-off-by: Waiman Long <longman@xxxxxxxxxx> --- kernel/rcu/refscale.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c index 1970ce5f22d4..e365d6f8c139 100644 --- a/kernel/rcu/refscale.c +++ b/kernel/rcu/refscale.c @@ -1107,12 +1107,11 @@ ref_scale_init(void) VERBOSE_SCALEOUT("Starting %d reader threads", nreaders); for (i = 0; i < nreaders; i++) { + init_waitqueue_head(&(reader_tasks[i].wq));Running checkpatch.pl tool with the " --strict" option, it complained that "CHECK: Unnecessary parentheses around reader_tasks[i].wq". I know that you just moved the code position. The tool should have complained the original code. 😊 Other than that, this patch LGTM. Reviewed-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx> Thanks! -Qiuxu
Thanks for the review. I will do --strict test next time. Cheers, Longman
firsterr = torture_create_kthread(ref_scale_reader, (void *)i, reader_tasks[i].task); if (torture_init_error(firsterr)) goto unwind; - - init_waitqueue_head(&(reader_tasks[i].wq)); } // Main Task -- 2.31.1
