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authorMel Gorman <mel@csn.ul.ie>2011-01-13 18:47:21 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 20:32:48 -0500
commit29c1f677d424e8c5683a837fc4f03fc9f19201d7 (patch)
tree97f257ab279cc000e02a1a58fa0869fb405f26cd /mm
parent22e5c47ee238abe636655c3862ed28d6eb084ad4 (diff)
mm: migration: use rcu_dereference_protected when dereferencing the radix tree slot during file page migration
migrate_pages() -> unmap_and_move() only calls rcu_read_lock() for anonymous pages, as introduced by git commit 989f89c57e6361e7d16fbd9572b5da7d313b073d ("fix rcu_read_lock() in page migraton"). The point of the RCU protection there is part of getting a stable reference to anon_vma and is only held for anon pages as file pages are locked which is sufficient protection against freeing. However, while a file page's mapping is being migrated, the radix tree is double checked to ensure it is the expected page. This uses radix_tree_deref_slot() -> rcu_dereference() without the RCU lock held triggering the following warning. [ 173.674290] =================================================== [ 173.676016] [ INFO: suspicious rcu_dereference_check() usage. ] [ 173.676016] --------------------------------------------------- [ 173.676016] include/linux/radix-tree.h:145 invoked rcu_dereference_check() without protection! [ 173.676016] [ 173.676016] other info that might help us debug this: [ 173.676016] [ 173.676016] [ 173.676016] rcu_scheduler_active = 1, debug_locks = 0 [ 173.676016] 1 lock held by hugeadm/2899: [ 173.676016] #0: (&(&inode->i_data.tree_lock)->rlock){..-.-.}, at: [<c10e3d2b>] migrate_page_move_mapping+0x40/0x1ab [ 173.676016] [ 173.676016] stack backtrace: [ 173.676016] Pid: 2899, comm: hugeadm Not tainted 2.6.37-rc5-autobuild [ 173.676016] Call Trace: [ 173.676016] [<c128cc01>] ? printk+0x14/0x1b [ 173.676016] [<c1063502>] lockdep_rcu_dereference+0x7d/0x86 [ 173.676016] [<c10e3db5>] migrate_page_move_mapping+0xca/0x1ab [ 173.676016] [<c10e41ad>] migrate_page+0x23/0x39 [ 173.676016] [<c10e491b>] buffer_migrate_page+0x22/0x107 [ 173.676016] [<c10e48f9>] ? buffer_migrate_page+0x0/0x107 [ 173.676016] [<c10e425d>] move_to_new_page+0x9a/0x1ae [ 173.676016] [<c10e47e6>] migrate_pages+0x1e7/0x2fa This patch introduces radix_tree_deref_slot_protected() which calls rcu_dereference_protected(). Users of it must pass in the mapping->tree_lock that is protecting this dereference. Holding the tree lock protects against parallel updaters of the radix tree meaning that rcu_dereference_protected is allowable. [akpm@linux-foundation.org: remove unneeded casts] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Milton Miller <miltonm@bga.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: <stable@kernel.org> [2.6.37.early] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/migrate.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index 1a531b760b3b..89a6bc8cd307 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -248,7 +248,7 @@ static int migrate_page_move_mapping(struct address_space *mapping,
248 248
249 expected_count = 2 + page_has_private(page); 249 expected_count = 2 + page_has_private(page);
250 if (page_count(page) != expected_count || 250 if (page_count(page) != expected_count ||
251 (struct page *)radix_tree_deref_slot(pslot) != page) { 251 radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
252 spin_unlock_irq(&mapping->tree_lock); 252 spin_unlock_irq(&mapping->tree_lock);
253 return -EAGAIN; 253 return -EAGAIN;
254 } 254 }
@@ -320,7 +320,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
320 320
321 expected_count = 2 + page_has_private(page); 321 expected_count = 2 + page_has_private(page);
322 if (page_count(page) != expected_count || 322 if (page_count(page) != expected_count ||
323 (struct page *)radix_tree_deref_slot(pslot) != page) { 323 radix_tree_deref_slot_protected(pslot, &mapping->tree_lock) != page) {
324 spin_unlock_irq(&mapping->tree_lock); 324 spin_unlock_irq(&mapping->tree_lock);
325 return -EAGAIN; 325 return -EAGAIN;
326 } 326 }