mm: move migrate_prep out from under mmap_sem
Move the migrate_prep outside the mmap_sem for the following system calls
1. sys_move_pages
2. sys_migrate_pages
3. sys_mbind()
It really does not matter when we flush the lru. The system is free to
add pages onto the lru even during migration which will make the page
migration either skip the page (mbind, migrate_pages) or return a busy
state (move_pages).
Fixes this lockdep warning (and potential deadlock):
Some VM place has
mmap_sem -> kevent_wq via lru_add_drain_all()
net/core/dev.c::dev_ioctl() has
rtnl_lock -> mmap_sem (*) the ioctl has copy_from_user() and it can do page fault.
linkwatch_event has
kevent_wq -> rtnl_lock
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 36f4257..e9493b1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -489,12 +489,6 @@
int err;
struct vm_area_struct *first, *vma, *prev;
- if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
-
- err = migrate_prep();
- if (err)
- return ERR_PTR(err);
- }
first = find_vma(mm, start);
if (!first)
@@ -809,9 +803,13 @@
const nodemask_t *from_nodes, const nodemask_t *to_nodes, int flags)
{
int busy = 0;
- int err = 0;
+ int err;
nodemask_t tmp;
+ err = migrate_prep();
+ if (err)
+ return err;
+
down_read(&mm->mmap_sem);
err = migrate_vmas(mm, from_nodes, to_nodes, flags);
@@ -974,6 +972,12 @@
start, start + len, mode, mode_flags,
nmask ? nodes_addr(*nmask)[0] : -1);
+ if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
+
+ err = migrate_prep();
+ if (err)
+ return err;
+ }
down_write(&mm->mmap_sem);
vma = check_range(mm, start, end, nmask,
flags | MPOL_MF_INVERT, &pagelist);