Re: [PATCH 2/3] mm, notifier: Catch sleeping/blocking for !blockable

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Am 23.11.18 um 09:46 schrieb Daniel Vetter:
On Thu, Nov 22, 2018 at 06:55:17PM +0000, Koenig, Christian wrote:
Am 22.11.18 um 17:51 schrieb Daniel Vetter:
We need to make sure implementations don't cheat and don't have a
possible schedule/blocking point deeply burried where review can't
catch it.

I'm not sure whether this is the best way to make sure all the
might_sleep() callsites trigger, and it's a bit ugly in the code flow.
But it gets the job done.

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: "Christian König" <christian.koenig@xxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
   mm/mmu_notifier.c | 8 +++++++-
   1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 59e102589a25..4d282cfb296e 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -185,7 +185,13 @@ int __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
   	id = srcu_read_lock(&srcu);
   	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
   		if (mn->ops->invalidate_range_start) {
-			int _ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
+			int _ret;
+
+			if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !blockable)
+				preempt_disable();
+			_ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
+			if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !blockable)
+				preempt_enable();
Just for the sake of better documenting this how about adding this to
include/linux/kernel.h right next to might_sleep():

#define disallow_sleeping_if(cond)    for((cond) ? preempt_disable() :
(void)0; (cond); preempt_disable())

(Just from the back of my head, might contain peanuts and/or hints of
errors).
I think these magic for blocks aren't used in the kernel. goto breaks
them, and we use goto a lot.

Yeah, good argument.

I think a disallow/allow_sleep() pair with
the conditional preept_disable/enable() calls would be nice though. I can
do that if the overall idea sticks.

Sounds like a good idea to me as well.

Christian.

-Daniel

Christian.

   			if (_ret) {
   				pr_info("%pS callback failed with %d in %sblockable context.\n",
   						mn->ops->invalidate_range_start, _ret,




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