mm: introduce FAULT_FLAG_INTERRUPTIBLE

handle_userfaultfd() is currently the only one place in the kernel page
fault procedures that can respond to non-fatal userspace signals.  It was
trying to detect such an allowance by checking against USER & KILLABLE
flags, which was "un-official".

In this patch, we introduced a new flag (FAULT_FLAG_INTERRUPTIBLE) to show
that the fault handler allows the fault procedure to respond even to
non-fatal signals.  Meanwhile, add this new flag to the default fault
flags so that all the page fault handlers can benefit from the new flag.
With that, replacing the userfault check to this one.

Since the line is getting even longer, clean up the fault flags a bit too
to ease TTY users.

Although we've got a new flag and applied it, we shouldn't have any
functional change with this patch so far.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Brian Geffon <bgeffon@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Link: http://lkml.kernel.org/r/20200220195348.16302-1-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 888272621f38434ea66ee8157f7984364bb083ad..c076d3295958ae0bf80ed9583ce0ca875a5d200a 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -462,9 +462,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
        uwq.ctx = ctx;
        uwq.waken = false;
 
-       return_to_userland =
-               (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
-               (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
+       return_to_userland = vmf->flags & FAULT_FLAG_INTERRUPTIBLE;
        blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
                         TASK_KILLABLE;
 

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 60f1192ee06e299f9a67f7f8a9ec12d7ed0b1577..7eeabc37ec8775e5559ed7465b09da94ede041da 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -381,22 +381,38 @@ extern unsigned int kobjsize(const void *objp);
  */
 extern pgprot_t protection_map[16];
 
-#define FAULT_FLAG_WRITE       0x01    /* Fault was a write access */
-#define FAULT_FLAG_MKWRITE     0x02    /* Fault was mkwrite of existing pte */
-#define FAULT_FLAG_ALLOW_RETRY 0x04    /* Retry fault if blocking */
-#define FAULT_FLAG_RETRY_NOWAIT        0x08    /* Don't drop mmap_sem and wait when retrying */
-#define FAULT_FLAG_KILLABLE    0x10    /* The fault task is in SIGKILL killable region */
-#define FAULT_FLAG_TRIED       0x20    /* Second try */
-#define FAULT_FLAG_USER                0x40    /* The fault originated in userspace */
-#define FAULT_FLAG_REMOTE      0x80    /* faulting for non current tsk/mm */
-#define FAULT_FLAG_INSTRUCTION  0x100  /* The fault was during an instruction fetch */
+/**
+ * Fault flag definitions.
+ *
+ * @FAULT_FLAG_WRITE: Fault was a write fault.
+ * @FAULT_FLAG_MKWRITE: Fault was mkwrite of existing PTE.
+ * @FAULT_FLAG_ALLOW_RETRY: Allow to retry the fault if blocked.
+ * @FAULT_FLAG_RETRY_NOWAIT: Don't drop mmap_sem and wait when retrying.
+ * @FAULT_FLAG_KILLABLE: The fault task is in SIGKILL killable region.
+ * @FAULT_FLAG_TRIED: The fault has been tried once.
+ * @FAULT_FLAG_USER: The fault originated in userspace.
+ * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
+ * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
+ * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ */
+#define FAULT_FLAG_WRITE                       0x01
+#define FAULT_FLAG_MKWRITE                     0x02
+#define FAULT_FLAG_ALLOW_RETRY                 0x04
+#define FAULT_FLAG_RETRY_NOWAIT                        0x08
+#define FAULT_FLAG_KILLABLE                    0x10
+#define FAULT_FLAG_TRIED                       0x20
+#define FAULT_FLAG_USER                                0x40
+#define FAULT_FLAG_REMOTE                      0x80
+#define FAULT_FLAG_INSTRUCTION                 0x100
+#define FAULT_FLAG_INTERRUPTIBLE               0x200
 
 /*
  * The default fault flags that should be used by most of the
  * arch-specific page fault handlers.
  */
 #define FAULT_FLAG_DEFAULT  (FAULT_FLAG_ALLOW_RETRY | \
-                            FAULT_FLAG_KILLABLE)
+                            FAULT_FLAG_KILLABLE | \
+                            FAULT_FLAG_INTERRUPTIBLE)
 
 #define FAULT_FLAG_TRACE \
        { FAULT_FLAG_WRITE,             "WRITE" }, \
@@ -407,7 +423,8 @@ extern pgprot_t protection_map[16];
        { FAULT_FLAG_TRIED,             "TRIED" }, \
        { FAULT_FLAG_USER,              "USER" }, \
        { FAULT_FLAG_REMOTE,            "REMOTE" }, \
-       { FAULT_FLAG_INSTRUCTION,       "INSTRUCTION" }
+       { FAULT_FLAG_INSTRUCTION,       "INSTRUCTION" }, \
+       { FAULT_FLAG_INTERRUPTIBLE,     "INTERRUPTIBLE" }
 
 /*
  * vm_fault is filled by the the pagefault handler and passed to the vma's