From 34c9cfcde29b938c416924ee6ec3519270bc2238 Mon Sep 17 00:00:00 2001 From: Nam Cao Date: Fri, 7 Aug 2026 19:24:30 -0600 Subject: [PATCH] riscv: unaligned: stop using kthread for check_vector_unaligned_access() A kthread is used to run check_vector_unaligned_access() to optimize boot time, allowing the kernel to continue booting without waiting for the unaligned vector speed probe to finish. However, this asynchronous approach introduces several complications. First, the kthread may not complete before a user reads vDSO data, resulting in incorrect values. This was previously addressed by commit 5d15d2ad36b0 ("riscv: hwprobe: Fix stale vDSO data for late-initialized keys at boot"), which added complex synchronization between the kthread and vDSO reads. Second, it was discovered that the kthread may not finish before vec_check_unaligned_access_speed_all_cpus() (marked with __init) is freed, triggering a page fault. These issues raise the question of whether the kthread is worth the added complexity. A past boot time regression report was actually unrelated to synchronous probing; it was caused by the probe running serially. Since switching to a parallel probe, no further complaints have been made. Furthermore, the unaligned scalar access speed probe takes the same amount of time, runs synchronously, and has caused no issues. Testing shows no noticeable boot time slowdown when running the vector probe synchronously (0.464474s with kthread vs. 0.457991s without). Remove the kthread usage and run the probe synchronously. This simplifies the boot flow and allows for the revert of commit 5d15d2ad36b0 ("riscv: hwprobe: Fix stale vDSO data for late-initialized keys at boot") Reported-by: Anirudh Srinivasan Closes: https://lore.kernel.org/linux-riscv/20260612-vec_unaligned_drop_init-v1-1-df969210ae34@oss.tenstorrent.com/ Fixes: e7c9d66e313b ("RISC-V: Report vector unaligned access speed hwprobe") Cc: stable@vger.kernel.org Signed-off-by: Nam Cao Acked-by: Jesse Taube Tested-by: Anirudh Srinivasan Link: https://patch.msgid.link/1c378963f27c5960e8a57c50b8b444d30954cb54.1781666867.git.namcao@linutronix.de [pjw@kernel.org: updated to apply; adjusted Fixes: tag; fixed my own manual patch application error] Signed-off-by: Paul Walmsley --- arch/riscv/kernel/unaligned_access_speed.c | 19 ++----------------- 1 file changed, 2 insertions(+), 17 deletions(-) diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c index 36201613d2ca..67f1a0371659 100644 --- a/arch/riscv/kernel/unaligned_access_speed.c +++ b/arch/riscv/kernel/unaligned_access_speed.c @@ -6,7 +6,6 @@ #include #include #include -#include #include #include #include @@ -288,18 +287,9 @@ static void check_vector_unaligned_access(struct work_struct *work __always_unus __free_pages(page, MISALIGNED_BUFFER_ORDER); } -/* Measure unaligned access speed on all CPUs present at boot in parallel. */ -static int vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused) -{ - schedule_on_each_cpu(check_vector_unaligned_access); - riscv_hwprobe_complete_async_probe(); - - return 0; -} #else /* CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS */ -static int vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused) +static void check_vector_unaligned_access(struct work_struct *work __always_unused) { - return 0; } #endif @@ -387,12 +377,7 @@ static int __init check_unaligned_access_all_cpus(void) per_cpu(vector_misaligned_access, cpu) = unaligned_vector_speed_param; } else if (!check_vector_unaligned_access_emulated_all_cpus() && IS_ENABLED(CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS)) { - riscv_hwprobe_register_async_probe(); - if (IS_ERR(kthread_run(vec_check_unaligned_access_speed_all_cpus, - NULL, "vec_check_unaligned_access_speed_all_cpus"))) { - pr_warn("Failed to create vec_unalign_check kthread\n"); - riscv_hwprobe_complete_async_probe(); - } + schedule_on_each_cpu(check_vector_unaligned_access); } /*