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authorThomas Gleixner <tglx@linutronix.de>2020-11-03 10:27:19 +0100
committerThomas Gleixner <tglx@linutronix.de>2020-11-06 23:14:55 +0100
commit389755c250814185938f5b04334a4f0184c30647 (patch)
tree3ce03d2f790b6a77c87398c161329341ee5e8ca5 /mm/highmem.c
parent298fa1ad5571f59cb3ca5497a9455f36867f065e (diff)
highmem: Make DEBUG_HIGHMEM functional
For some obscure reason when CONFIG_DEBUG_HIGHMEM is enabled the stack depth is increased from 20 to 41. But the only thing DEBUG_HIGHMEM does is to enable a few BUG_ON()'s in the mapping code. That's a leftover from the historical mapping code which had fixed entries for various purposes. DEBUG_HIGHMEM inserted guard mappings between the map types. But that got all ditched when kmap_atomic() switched to a stack based map management. Though the WITH_KM_FENCE magic survived without being functional. All the thing does today is to increase the stack depth. Add a working implementation to the generic kmap_local* implementation. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linuxfoundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Andrew Morton <akpm@linux-foundation.org> Link: https://lore.kernel.org/r/20201103095857.268258322@linutronix.de
Diffstat (limited to 'mm/highmem.c')
-rw-r--r--mm/highmem.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/mm/highmem.c b/mm/highmem.c
index bb4ce13ee7e7..67d2d5983cb0 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -376,9 +376,19 @@ EXPORT_SYMBOL(kunmap_high);
static DEFINE_PER_CPU(int, __kmap_local_idx);
+/*
+ * With DEBUG_HIGHMEM the stack depth is doubled and every second
+ * slot is unused which acts as a guard page
+ */
+#ifdef CONFIG_DEBUG_HIGHMEM
+# define KM_INCR 2
+#else
+# define KM_INCR 1
+#endif
+
static inline int kmap_local_idx_push(void)
{
- int idx = __this_cpu_inc_return(__kmap_local_idx) - 1;
+ int idx = __this_cpu_add_return(__kmap_local_idx, KM_INCR) - 1;
WARN_ON_ONCE(in_irq() && !irqs_disabled());
BUG_ON(idx >= KM_MAX_IDX);
@@ -392,7 +402,7 @@ static inline int kmap_local_idx(void)
static inline void kmap_local_idx_pop(void)
{
- int idx = __this_cpu_dec_return(__kmap_local_idx);
+ int idx = __this_cpu_sub_return(__kmap_local_idx, KM_INCR);
BUG_ON(idx < 0);
}