Forcing in_interrupt() to return true if we're not in a bona fide
interrupt confuses the softirq code. This fixes warnings like:
NOHZ: local_softirq_pending 282
that can happen when running things like selftests/x86.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 959274753857 ("x86, traps: Track entry into and exit from IST context")
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
This is intended for x86/urgent.
arch/x86/kernel/traps.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d1590486204a..25a905674acd 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -96,6 +96,20 @@ static inline void cond_local_irq_disable(struct pt_regs *regs)
local_irq_disable();
}
+/*
+ * We want to cause in_atomic() to return true while in an IST handler
+ * so that attempts to schedule will warn.
+ *
+ * We cannot add use HARDIRQ_OFFSET or otherwise cause in_interrupt() to
+ * return true: the softirq code assumes that in_interrupt() only
+ * returns true if we will soon execute softirqs, and we can't do that
+ * if an IST entry interrupts kernel code with interrupts disabled.
+ *
+ * Using 3 * PREEMPT_OFFSET instead of just PREEMPT_OFFSET is pure
+ * paranoia.
+ */
+#define IST_OFFSET (3 * PREEMPT_OFFSET)
+
void ist_enter(struct pt_regs *regs)
{
if (user_mode(regs)) {
@@ -116,7 +130,7 @@ void ist_enter(struct pt_regs *regs)
* on x86_64 and entered from user mode, in which case we're
* still atomic unless ist_begin_non_atomic is called.
*/
- preempt_count_add(HARDIRQ_OFFSET);
+ preempt_count_add(IST_OFFSET);
/* This code is a bit fragile. Test it. */
RCU_LOCKDEP_WARN(!rcu_is_watching(), "ist_enter didn't work");
@@ -124,7 +138,7 @@ void ist_enter(struct pt_regs *regs)
void ist_exit(struct pt_regs *regs)
{
- preempt_count_sub(HARDIRQ_OFFSET);
+ preempt_count_sub(IST_OFFSET);
if (!user_mode(regs))
rcu_nmi_exit();
@@ -155,7 +169,7 @@ void ist_begin_non_atomic(struct pt_regs *regs)
BUG_ON((unsigned long)(current_top_of_stack() -
current_stack_pointer()) >= THREAD_SIZE);
- preempt_count_sub(HARDIRQ_OFFSET);
+ preempt_count_sub(IST_OFFSET);
}
/**
@@ -165,7 +179,7 @@ void ist_begin_non_atomic(struct pt_regs *regs)
*/
void ist_end_non_atomic(void)
{
- preempt_count_add(HARDIRQ_OFFSET);
+ preempt_count_add(IST_OFFSET);
}
static nokprobe_inline int
--
2.5.5
--
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