On 11/05/2016 06:43 AM, Joel Fernandes wrote:

On Mon, Oct 24, 2016 at 8:44 AM, Andrey Ryabinin
[off-list ref] wrote:

quoted

On 10/22/2016 06:17 PM, Christoph Hellwig wrote:

quoted

We want to be able to use a sleeping lock for freeing vmap to keep
latency down.  For this we need to use the deferred vfree mechanisms
no only from interrupt, but from any atomic context.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/vmalloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a4e2cec..bcc1a64 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c

@@ -1509,7 +1509,7 @@ void vfree(const void *addr)

      if (!addr)
              return;
-     if (unlikely(in_interrupt())) {
+     if (unlikely(in_atomic())) {

in_atomic() cannot always detect atomic context, thus it shouldn't be used here.
You can add something like vfree_in_atomic() and use it in atomic call sites.

So because in_atomic doesn't work for !CONFIG_PREEMPT kernels, can we
always defer the work in these cases?

So for non-preemptible kernels, we always defer:

if (!IS_ENABLED(CONFIG_PREEMPT) || in_atomic()) {
  // defer
}

Is this fine? Or any other ideas?

What's wrong with my idea?
We can add vfree_in_atomic() and use it to free vmapped stacks
and for any other places where vfree() used 'in_atomict() && !in_interrupt()' context.

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