percpu: convert spin_lock_irq to spin_lock_irqsave

This fixes boot failure with the alpha-generic flavour, discussed in
https://lists.debian.org/debian-alpha/2018/12/msg00001.html and
https://salsa.debian.org/kernel-team/linux/merge_requests/79

debian/changelog

@@ -98,6 +98,8 @@ linux (4.19.17-1) UNRELEASED; urgency=medium
   * [i386] debian/control: Fix cross-compiler build-dependency
   * debian/README.source: Document how to run kconfigeditor2
   * [armhf,arm64] serial: 8250: Disable SERIAL_8250_DEPRECATED_OPTIONS
+  * percpu: convert spin_lock_irq to spin_lock_irqsave (fixes boot failure with
+    alpha-generic flavour)
 
   [ Marcin Juszkiewicz ]
   * [arm64] enable ARM_CCI_PMU so ARM_CCI400_PMU and ARM_CCI5xx_PMU options

debian/patches/bugfix/all/percpu-convert-spin_lock_irq-to-spin_lock_irqsave.patch

@@ -0,0 +1,49 @@
+From: Dennis Zhou <dennis@kernel.org>
+Date: Tue, 18 Dec 2018 08:42:27 -0800
+Subject: percpu: convert spin_lock_irq to spin_lock_irqsave.
+Origin: https://git.kernel.org/linus/6ab7d47bcbf0144a8cb81536c2cead4cde18acfe
+
+From Michael Cree:
+  "Bisection lead to commit b38d08f3181c ("percpu: restructure
+   locking") as being the cause of lockups at initial boot on
+   the kernel built for generic Alpha.
+
+   On a suggestion by Tejun Heo that:
+
+   So, the only thing I can think of is that it's calling
+   spin_unlock_irq() while irq handling isn't set up yet.
+   Can you please try the followings?
+
+   1. Convert all spin_[un]lock_irq() to
+      spin_lock_irqsave/unlock_irqrestore()."
+
+Fixes: b38d08f3181c ("percpu: restructure locking")
+Reported-and-tested-by: Michael Cree <mcree@orcon.net.nz>
+Acked-by: Tejun Heo <tj@kernel.org>
+Signed-off-by: Dennis Zhou <dennis@kernel.org>
+---
+ mm/percpu-km.c | 5 +++--
+ 1 file changed, 3 insertions(+), 2 deletions(-)
+
+--- a/mm/percpu-km.c
++++ b/mm/percpu-km.c
+@@ -50,6 +50,7 @@ static struct pcpu_chunk *pcpu_create_ch
+ 	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
+ 	struct pcpu_chunk *chunk;
+ 	struct page *pages;
++	unsigned long flags;
+ 	int i;
+ 
+ 	chunk = pcpu_alloc_chunk(gfp);
+@@ -68,9 +69,9 @@ static struct pcpu_chunk *pcpu_create_ch
+ 	chunk->data = pages;
+ 	chunk->base_addr = page_address(pages) - pcpu_group_offsets[0];
+ 
+-	spin_lock_irq(&pcpu_lock);
++	spin_lock_irqsave(&pcpu_lock, flags);
+ 	pcpu_chunk_populated(chunk, 0, nr_pages, false);
+-	spin_unlock_irq(&pcpu_lock);
++	spin_unlock_irqrestore(&pcpu_lock, flags);
+ 
+ 	pcpu_stats_chunk_alloc();
+ 	trace_percpu_create_chunk(chunk->base_addr);

debian/patches/series

@@ -101,6 +101,7 @@ bugfix/all/kbuild-include-addtree-remove-quotes-before-matching-path.patch
 debian/revert-objtool-fix-config_stack_validation-y-warning.patch
 bugfix/all/ipv6-Consider-sk_bound_dev_if-when-binding-a-socket-.patch
 bugfix/all/posix-cpu-timers-Unbreak-timer-rearming.patch
+bugfix/all/percpu-convert-spin_lock_irq-to-spin_lock_irqsave.patch
 
 # Miscellaneous features