From: Waiman Long <longman@redhat.com>
Date: Thu, 22 Sep 2022 10:56:22 -0400
Subject: tracing: Disable interrupt or preemption before acquiring
 arch_spinlock_t
Git-commit: c0a581d7126c0bbc96163276f585fd7b4e4d8d0e
Patch-mainline: v6.1-rc1
References: git-fixes

It was found that some tracing functions in kernel/trace/trace.c acquire
an arch_spinlock_t with preemption and irqs enabled. An example is the
tracing_saved_cmdlines_size_read() function which intermittently causes
a "BUG: using smp_processor_id() in preemptible" warning when the LTP
read_all_proc test is run.

That can be problematic in case preemption happens after acquiring the
lock. Add the necessary preemption or interrupt disabling code in the
appropriate places before acquiring an arch_spinlock_t.

The convention here is to disable preemption for trace_cmdline_lock and
interupt for max_lock.

Link: https://lkml.kernel.org/r/20220922145622.1744826-1-longman@redhat.com

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: stable@vger.kernel.org
Fixes: a35873a0993b ("tracing: Add conditional snapshot")
Fixes: 939c7a4f04fc ("tracing: Introduce saved_cmdlines_size file")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
[ppavlu:
* Strip the local_irq_disable()/local_irq_enable() additions for
  max_lock which are related to non-picked
  commit a35873a0993b ("tracing: Add conditional snapshot").
* Remove the lockdep_assert_preemption_disabled() assertion added
  to trace_save_cmdline() because it is not available. It requires
  commit 8fd8ad5c5dfc ("lockdep: Add preemption enabled/disabled assertion APIs").]
Acked-by: Petr Pavlu <petr.pavlu@suse.com>
---
 kernel/trace/trace.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d3005279165d..aed7ea6e6045 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2200,6 +2206,11 @@ static size_t tgid_map_max;
 
 #define SAVED_CMDLINES_DEFAULT 128
 #define NO_CMDLINE_MAP UINT_MAX
+/*
+ * Preemption must be disabled before acquiring trace_cmdline_lock.
+ * The various trace_arrays' max_lock must be acquired in a context
+ * where interrupt is disabled.
+ */
 static arch_spinlock_t trace_cmdline_lock = __ARCH_SPIN_LOCK_UNLOCKED;
 struct saved_cmdlines_buffer {
 	unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
@@ -2412,6 +2423,9 @@ static int trace_save_cmdline(struct task_struct *tsk)
 	 * the lock, but we also don't want to spin
 	 * nor do we want to disable interrupts,
 	 * so if we miss here, then better luck next time.
+	 *
+	 * This is called within the scheduler and wake up, so interrupts
+	 * had better been disabled and run queue lock been held.
 	 */
 	if (!arch_spin_trylock(&trace_cmdline_lock))
 		return 0;
@@ -5890,9 +5905,11 @@ tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf,
 	char buf[64];
 	int r;
 
+	preempt_disable();
 	arch_spin_lock(&trace_cmdline_lock);
 	r = scnprintf(buf, sizeof(buf), "%u\n", savedcmd->cmdline_num);
 	arch_spin_unlock(&trace_cmdline_lock);
+	preempt_enable();
 
 	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
@@ -5917,10 +5934,12 @@ static int tracing_resize_saved_cmdlines(unsigned int val)
 		return -ENOMEM;
 	}
 
+	preempt_disable();
 	arch_spin_lock(&trace_cmdline_lock);
 	savedcmd_temp = savedcmd;
 	savedcmd = s;
 	arch_spin_unlock(&trace_cmdline_lock);
+	preempt_enable();
 	free_saved_cmdlines_buffer(savedcmd_temp);
 
 	return 0;