From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
v5.15.133-rt70-rc1 stable review patch.
If anyone has any objections, please let me know.
-----------
__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@xxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230623201517.yw286Knb@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
(cherry picked from commit 4d1139baae8bc4fff3728d1d204bdb04c13dbe10)
Signed-off-by: Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>
---
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 33355028122a..174bcc23d5fd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6419,19 +6419,17 @@ 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));
@@ -6464,9 +6462,8 @@ 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
--
2.34.1
