Mel Gorman 29c1f677d4 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 989f89c57e ("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>		2011-01-13 17:32:48 -08:00
..
acpi
asm-generic	thp: mm: define MADV_NOHUGEPAGE	2011-01-13 17:32:47 -08:00
crypto
drm	Merge branch 'drm-radeon-ni' of ../drm-radeon-next into drm-core-next	2011-01-10 09:27:06 +10:00
keys
linux	mm: migration: use rcu_dereference_protected when dereferencing the radix tree slot during file page migration	2011-01-13 17:32:48 -08:00
math-emu
media	Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial	2011-01-13 10:05:56 -08:00
mtd
net	Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial	2011-01-13 10:05:56 -08:00
pcmcia
rdma
rxrpc
scsi	Merge branch 'for-2.6.38/core' of git://git.kernel.dk/linux-2.6-block	2011-01-13 10:45:01 -08:00
sound	Merge branch 'topic/asoc' into for-linus	2011-01-13 08:37:24 +01:00
trace	mm: vmscan: rename lumpy_mode to reclaim_mode	2011-01-13 17:32:34 -08:00
video
xen	Merge branch 'stable/xenbus' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen	2011-01-12 08:37:35 -08:00
Kbuild