The following commit has been merged into the core/mm branch of tip: Commit-ID: 389755c250814185938f5b04334a4f0184c30647 Gitweb: https://git.kernel.org/tip/389755c250814185938f5b04334a4f0184c30647 Author: Thomas Gleixner <[email protected]> AuthorDate: Tue, 03 Nov 2020 10:27:19 +01:00 Committer: Thomas Gleixner <[email protected]> CommitterDate: Fri, 06 Nov 2020 23:14:55 +01:00
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 <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Andrew Morton <[email protected]> Link: https://lore.kernel.org/r/[email protected] --- mm/highmem.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/highmem.c b/mm/highmem.c index bb4ce13..67d2d59 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); }
