lkml.org 
[lkml]   [2022]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v4 5/9] mm/hugetlb: Make userfaultfd_huge_must_wait() safe to pmd unshare
Date
We can take the hugetlb walker lock, here taking vma lock directly.

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
fs/userfaultfd.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 98ac37e34e3d..887e20472051 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -376,7 +376,8 @@ static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
*/
vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
{
- struct mm_struct *mm = vmf->vma->vm_mm;
+ struct vm_area_struct *vma = vmf->vma;
+ struct mm_struct *mm = vma->vm_mm;
struct userfaultfd_ctx *ctx;
struct userfaultfd_wait_queue uwq;
vm_fault_t ret = VM_FAULT_SIGBUS;
@@ -403,7 +404,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
*/
mmap_assert_locked(mm);

- ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
+ ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx)
goto out;

@@ -493,6 +494,15 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)

blocking_state = userfaultfd_get_blocking_state(vmf->flags);

+ /*
+ * Take the vma lock now, in order to safely call
+ * userfaultfd_huge_must_wait() later. Since acquiring the
+ * (sleepable) vma lock can modify the current task state, that
+ * must be before explicitly calling set_current_state().
+ */
+ if (is_vm_hugetlb_page(vma))
+ hugetlb_vma_lock_read(vma);
+
spin_lock_irq(&ctx->fault_pending_wqh.lock);
/*
* After the __add_wait_queue the uwq is visible to userland
@@ -507,13 +517,15 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
set_current_state(blocking_state);
spin_unlock_irq(&ctx->fault_pending_wqh.lock);

- if (!is_vm_hugetlb_page(vmf->vma))
+ if (!is_vm_hugetlb_page(vma))
must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
reason);
else
- must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
+ must_wait = userfaultfd_huge_must_wait(ctx, vma,
vmf->address,
vmf->flags, reason);
+ if (is_vm_hugetlb_page(vma))
+ hugetlb_vma_unlock_read(vma);
mmap_read_unlock(mm);

if (likely(must_wait && !READ_ONCE(ctx->released))) {
--
2.37.3
\
 
 \ /
  Last update: 2022-12-16 16:54    [W:0.056 / U:2.548 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site