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mm: move migrate_prep out from under mmap_sem

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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 <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Reported-by: Heiko Carstens <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Lee Schermerhorn <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Christoph Lameter 2008-11-06 12:53:30 -08:00 • committed by Linus Torvalds
commit 0aedadf91a
2 changed files with 12 additions and 8 deletions
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2
mm/migrate.c
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@ -841,12 +841,12 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
struct page_to_node *pp;
LIST_HEAD(pagelist);
migrate_prep();
down_read(&mm->mmap_sem);
/*
* Build a list of pages to migrate
*/
migrate_prep();
for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
struct vm_area_struct *vma;
struct page *page;