linux-kernel - Re: [PATCH 2/6] mm: mark all calls into the vmalloc subsystem as potentially sleeping

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Date:   Wed, 19 Oct 2016 18:31:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Christoph Hellwig <hch@....de>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Andrew Morton <akpm@...ux-foundation.org>, joelaf@...gle.com,
        jszhang@...vell.com, joaodias@...gle.com,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-rt-users@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] mm: mark all calls into the vmalloc subsystem as
        potentially sleeping

On Wed, Oct 19, 2016 at 08:34:40AM -0700, Andy Lutomirski wrote:
> 
> It would be quite awkward for a task stack to get freed from a
> sleepable context, because the obvious sleepable context is the task
> itself, and it still needs its stack.  This was true even in the old
> regime when task stacks were freed from RCU context.
> 
> But vfree has a magic automatic deferral mechanism.  Couldn't you make
> the non-deferred case might_sleep()?

But it's only magic from interrupt context..

Chris, does this patch make virtually mapped stack work for you again?

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f2481cb..942e02d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1533,7 +1533,7 @@ void vfree(const void *addr)
 
 	if (!addr)
 		return;
-	if (unlikely(in_interrupt())) {
+	if (in_interrupt() || in_atomic()) {
 		struct vfree_deferred *p = this_cpu_ptr(&vfree_deferred);
 		if (llist_add((struct llist_node *)addr, &p->list))
 			schedule_work(&p->wq);