+ lazy-tlb-consolidate-lazy-tlb-mm-switching-fix.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: lazy tlb: consolidate lazy tlb mm switching fix
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     lazy-tlb-consolidate-lazy-tlb-mm-switching-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lazy-tlb-consolidate-lazy-tlb-mm-switching-fix.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Nicholas Piggin <npiggin@gmail.com>
Subject: lazy tlb: consolidate lazy tlb mm switching fix
Date: Wed, 7 Jun 2023 10:56:22 +1000

Fix an upstream powerpc bug that was discovered with a WARN_ON added in
"lazy tlb: consolidate lazy tlb mm switching":

   Switching mm and tinkering with current->active_mm should be done with
    irqs disabled. There is a path where exit_lazy_flush_tlb can be called
    with irqs enabled:

        exit_lazy_flush_tlb
        flush_type_needed
        __flush_all_mm
        tlb_finish_mmu
        exit_mmap

    Which results in the switching being incorrectly with irqs enabled.

    Link: https://lore.kernel.org/linuxppc-dev/87a5xcgopc.fsf@mail.lhotse/T/#m105488939d0cd9f980978ed2fdeeb89bf731e673
    Fixes: a665eec0a22e1 ("powerpc/64s/radix: Fix mm_cpumask trimming race vs k>

I will send that fix upstream, which will end up conflicting with these.
The resolution will be to take akpm's side of the merge (with this patch).
Or drop the patch when it conflicts and I'll resend it rebased on the fix.

Link: https://lkml.kernel.org/r/20230607005622.583318-1-npiggin@gmail.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Cc: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/powerpc/mm/book3s64/radix_tlb.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/arch/powerpc/mm/book3s64/radix_tlb.c~lazy-tlb-consolidate-lazy-tlb-mm-switching-fix
+++ a/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -795,8 +795,16 @@ void exit_lazy_flush_tlb(struct mm_struc
 		goto out;
 
 	if (current->active_mm == mm) {
-		/* Is a kernel thread and is using mm as the lazy tlb */
+		unsigned long flags;
+
+		/*
+		 * It is a kernel thread and is using mm as the lazy tlb, so
+		 * switch it to init_mm. This is not always called from IPI
+		 * (e.g., flush_type_needed), so must disable irqs.
+		 */
+		local_irq_save(flags);
 		kthread_end_lazy_tlb_mm();
+		local_irq_restore(flags);
 	}
 
 	/*
_

Patches currently in -mm which might be from npiggin@gmail.com are

lazy-tlb-fix-hotplug-exit-race-with-mmu_lazy_tlb_shootdown.patch
lazy-tlb-consolidate-lazy-tlb-mm-switching.patch
lazy-tlb-consolidate-lazy-tlb-mm-switching-fix.patch