linux-kernel - [RFC v4 16/20] mm/spf: Don't call user fault callback in the speculative path

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Message-Id: <1497018069-17790-17-git-send-email-ldufour@linux.vnet.ibm.com>
Date:   Fri,  9 Jun 2017 16:21:05 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com
Subject: [RFC v4 16/20] mm/spf: Don't call user fault callback in the speculative path

The handle_userfault() function assumes that the mmap_sem is held
which is not true in the case of a speculative page fault handling.

When doing a speculative page fault, lets retry it in the usual path
to call handle_userfault().

Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
---
 mm/memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 27e44ebc5440..5b158549789b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3005,6 +3005,8 @@ static int do_anonymous_page(struct vm_fault *vmf)
 		/* Deliver the page fault to userland, check inside PT lock */
 		if (userfaultfd_missing(vma)) {
 			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+				return VM_FAULT_RETRY;
 			return handle_userfault(vmf, VM_UFFD_MISSING);
 		}
 		goto setpte;
@@ -3045,6 +3047,8 @@ static int do_anonymous_page(struct vm_fault *vmf)
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
 		mem_cgroup_cancel_charge(page, memcg, false);
 		put_page(page);
+		if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+			return VM_FAULT_RETRY;
 		return handle_userfault(vmf, VM_UFFD_MISSING);
 	}
 
-- 
2.7.4