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| author | Thomas Gleixner <tglx@linutronix.de> | 2020-11-03 10:27:19 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-11-06 23:14:55 +0100 |
| commit | 389755c250814185938f5b04334a4f0184c30647 (patch) | |
| tree | 3ce03d2f790b6a77c87398c161329341ee5e8ca5 /mm/highmem.c | |
| parent | 298fa1ad5571f59cb3ca5497a9455f36867f065e (diff) | |
| download | linux-389755c250814185938f5b04334a4f0184c30647.tar.bz2 | |
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.c | 14 |
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); } |