• Mel Gorman's avatar
    mm: migration: use rcu_dereference_protected when dereferencing the radix tree... · 29c1f677
    Mel Gorman authored
    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
    989f89c5 ("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: default avatarMel 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: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    29c1f677
migrate.c 32 KB