mirror of
https://github.com/OpenVoiceOS/OpenVoiceOS
synced 2025-02-23 07:07:39 +01:00
97 lines
3.8 KiB
Diff
97 lines
3.8 KiB
Diff
From 295da0c59de4794e746f56b1567e3188f9addc00 Mon Sep 17 00:00:00 2001
|
|
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
Date: Fri, 23 Jun 2023 22:15:17 +0200
|
|
Subject: [PATCH 58/62] mm/page_alloc: Use write_seqlock_irqsave() instead
|
|
write_seqlock() + local_irq_save().
|
|
|
|
__build_all_zonelists() acquires zonelist_update_seq by first disabling
|
|
interrupts via local_irq_save() and then acquiring the seqlock with
|
|
write_seqlock(). This is troublesome and leads to problems on
|
|
PREEMPT_RT. The problem is that the inner spinlock_t becomes a sleeping
|
|
lock on PREEMPT_RT and must not be acquired with disabled interrupts.
|
|
|
|
The API provides write_seqlock_irqsave() which does the right thing in
|
|
one step.
|
|
printk_deferred_enter() has to be invoked in non-migrate-able context to
|
|
ensure that deferred printing is enabled and disabled on the same CPU.
|
|
This is the case after zonelist_update_seq has been acquired.
|
|
|
|
There was discussion on the first submission that the order should be:
|
|
local_irq_disable();
|
|
printk_deferred_enter();
|
|
write_seqlock();
|
|
|
|
to avoid pitfalls like having an unaccounted printk() coming from
|
|
write_seqlock_irqsave() before printk_deferred_enter() is invoked. The
|
|
only origin of such a printk() can be a lockdep splat because the
|
|
lockdep annotation happens after the sequence count is incremented.
|
|
This is exceptional and subject to change.
|
|
|
|
It was also pointed that PREEMPT_RT can be affected by the printk
|
|
problem since its write_seqlock_irqsave() does not really disable
|
|
interrupts. This isn't the case because PREEMPT_RT's printk
|
|
implementation differs from the mainline implementation in two important
|
|
aspects:
|
|
- Printing happens in a dedicated threads and not at during the
|
|
invocation of printk().
|
|
- In emergency cases where synchronous printing is used, a different
|
|
driver is used which does not use tty_port::lock.
|
|
|
|
Acquire zonelist_update_seq with write_seqlock_irqsave() and then defer
|
|
printk output.
|
|
|
|
Fixes: 1007843a91909 ("mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock")
|
|
Acked-by: Michal Hocko <mhocko@suse.com>
|
|
Reviewed-by: David Hildenbrand <david@redhat.com>
|
|
Link: https://lore.kernel.org/r/20230623201517.yw286Knb@linutronix.de
|
|
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
|
(cherry picked from commit 4d1139baae8bc4fff3728d1d204bdb04c13dbe10)
|
|
Signed-off-by: Clark Williams <clark.williams@gmail.com>
|
|
---
|
|
mm/page_alloc.c | 15 ++++++---------
|
|
1 file changed, 6 insertions(+), 9 deletions(-)
|
|
|
|
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
|
|
index 4583f8a42d91..835b69a64f4f 100644
|
|
--- a/mm/page_alloc.c
|
|
+++ b/mm/page_alloc.c
|
|
@@ -6588,19 +6588,17 @@ static void __build_all_zonelists(void *data)
|
|
unsigned long flags;
|
|
|
|
/*
|
|
- * Explicitly disable this CPU's interrupts before taking seqlock
|
|
- * to prevent any IRQ handler from calling into the page allocator
|
|
- * (e.g. GFP_ATOMIC) that could hit zonelist_iter_begin and livelock.
|
|
+ * The zonelist_update_seq must be acquired with irqsave because the
|
|
+ * reader can be invoked from IRQ with GFP_ATOMIC.
|
|
*/
|
|
- local_irq_save(flags);
|
|
+ write_seqlock_irqsave(&zonelist_update_seq, flags);
|
|
/*
|
|
- * Explicitly disable this CPU's synchronous printk() before taking
|
|
- * seqlock to prevent any printk() from trying to hold port->lock, for
|
|
+ * Also disable synchronous printk() to prevent any printk() from
|
|
+ * trying to hold port->lock, for
|
|
* tty_insert_flip_string_and_push_buffer() on other CPU might be
|
|
* calling kmalloc(GFP_ATOMIC | __GFP_NOWARN) with port->lock held.
|
|
*/
|
|
printk_deferred_enter();
|
|
- write_seqlock(&zonelist_update_seq);
|
|
|
|
#ifdef CONFIG_NUMA
|
|
memset(node_load, 0, sizeof(node_load));
|
|
@@ -6637,9 +6635,8 @@ static void __build_all_zonelists(void *data)
|
|
#endif
|
|
}
|
|
|
|
- write_sequnlock(&zonelist_update_seq);
|
|
printk_deferred_exit();
|
|
- local_irq_restore(flags);
|
|
+ write_sequnlock_irqrestore(&zonelist_update_seq, flags);
|
|
}
|
|
|
|
static noinline void __init
|
|
--
|
|
2.43.0
|
|
|