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