The patch titled
Subject: mm/swap_slots.c: don't disable preemption while taking the per-CPU cache
has been removed from the -mm tree. Its filename was
mm-swap-dont-disable-preemption-while-taking-the-per-cpu-cache.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: mm/swap_slots.c: don't disable preemption while taking the per-CPU cache
get_cpu_var() disables preemption and returns the per-CPU version of the
variable. Disabling preemption is useful to ensure atomic access to the
variable within the critical section.
In this case however, after the per-CPU version of the variable is
obtained the ->free_lock is acquired. For that reason it seems the raw
accessor could be used. It only seems that ->slots_ret should be retested
(because with disabled preemption this variable can not be set to NULL
otherwise).
This popped up during PREEMPT-RT testing because it tries to take
spinlocks in a preempt disabled section. In RT, spinlocks can sleep.
Link: http://lkml.kernel.org/r/20170623114755.2ebxdysacvgxzott@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ying Huang <ying.huang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap_slots.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff -puN mm/swap_slots.c~mm-swap-dont-disable-preemption-while-taking-the-per-cpu-cache mm/swap_slots.c
--- a/mm/swap_slots.c~mm-swap-dont-disable-preemption-while-taking-the-per-cpu-cache
+++ a/mm/swap_slots.c
@@ -273,11 +273,11 @@ int free_swap_slot(swp_entry_t entry)
{
struct swap_slots_cache *cache;
- cache = &get_cpu_var(swp_slots);
+ cache = raw_cpu_ptr(&swp_slots);
if (use_swap_slot_cache && cache->slots_ret) {
spin_lock_irq(&cache->free_lock);
/* Swap slots cache may be deactivated before acquiring lock */
- if (!use_swap_slot_cache) {
+ if (!use_swap_slot_cache || !cache->slots_ret) {
spin_unlock_irq(&cache->free_lock);
goto direct_free;
}
@@ -297,7 +297,6 @@ int free_swap_slot(swp_entry_t entry)
direct_free:
swapcache_free_entries(&entry, 1);
}
- put_cpu_var(swp_slots);
return 0;
}
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
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