From 3f9b5dfbc444cb7a8ce68254b348eed6d73c5bde Mon Sep 17 00:00:00 2001 From: Luo Gengkun Date: Tue, 19 Aug 2025 10:51:52 +0000 Subject: [PATCH] tracing: Fix tracing_marker may trigger page fault during preempt_disable [ Upstream commit 3d62ab32df065e4a7797204a918f6489ddb8a237 ] Both tracing_mark_write and tracing_mark_raw_write call __copy_from_user_inatomic during preempt_disable. But in some case, __copy_from_user_inatomic may trigger page fault, and will call schedule() subtly. And if a task is migrated to other cpu, the following warning will be trigger: if (RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing))) An example can illustrate this issue: process flow CPU --------------------------------------------------------------------- tracing_mark_raw_write(): cpu:0 ... ring_buffer_lock_reserve(): cpu:0 ... cpu = raw_smp_processor_id() cpu:0 cpu_buffer = buffer->buffers[cpu] cpu:0 ... ... __copy_from_user_inatomic(): cpu:0 ... # page fault do_mem_abort(): cpu:0 ... # Call schedule schedule() cpu:0 ... # the task schedule to cpu1 __buffer_unlock_commit(): cpu:1 ... ring_buffer_unlock_commit(): cpu:1 ... cpu = raw_smp_processor_id() cpu:1 cpu_buffer = buffer->buffers[cpu] cpu:1 As shown above, the process will acquire cpuid twice and the return values are not the same. To fix this problem using copy_from_user_nofault instead of __copy_from_user_inatomic, as the former performs 'access_ok' before copying. Link: https://lore.kernel.org/20250819105152.2766363-1-luogengkun@huaweicloud.com Fixes: 656c7f0d2d2b ("tracing: Replace kmap with copy_from_user() in trace_marker writing") Signed-off-by: Luo Gengkun Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google) Signed-off-by: Sasha Levin --- kernel/trace/trace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ba3358eef34b..87a43c0f9076 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6949,7 +6949,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, entry = ring_buffer_event_data(event); entry->ip = _THIS_IP_; - len = __copy_from_user_inatomic(&entry->buf, ubuf, cnt); + len = copy_from_user_nofault(&entry->buf, ubuf, cnt); if (len) { memcpy(&entry->buf, FAULTED_STR, FAULTED_SIZE); cnt = FAULTED_SIZE; @@ -7020,7 +7020,7 @@ tracing_mark_raw_write(struct file *filp, const char __user *ubuf, entry = ring_buffer_event_data(event); - len = __copy_from_user_inatomic(&entry->id, ubuf, cnt); + len = copy_from_user_nofault(&entry->id, ubuf, cnt); if (len) { entry->id = -1; memcpy(&entry->buf, FAULTED_STR, FAULTED_SIZE);