[RFC][PATCH] fix dm_any_congested() to properly sync up with suspend code path

[Chandra Seetharaman <sekharan@us.ibm.com>]

dm_any_congested() just checks for the DMF_BLOCK_IO and has no
code to make sure that suspend waits for dm_any_congested() to
complete.

This leads to a case where the table_destroy() and free_multipath()
and some other sleeping functions are called (thru dm_table_put())
from dm_any_congested.

This leads to 2 problems:
1. Sleeping functions called from congested code, whose caller
   holds a spin lock.
2. An ABBA deadlock between pdflush and multipathd. The two locks
   in contention are inode lock and kernel lock.
   Here is the crash analysis:
PID: 16879  TASK: ffff81013a06a140  CPU: 3   COMMAND: "pdflush"
Owns inode_lock and waiting for kernel_sem

PID: 8299   TASK: ffff81024f03e100  CPU: 2   COMMAND: "multipathd"
Owns kernel_sem and waiting for inode_lock.


PID: 8299   TASK: ffff81024f03e100  CPU: 2   COMMAND: "multipathd"^M
 #0 [ffff81024ad338c8] schedule at ffffffff8128534c^M
 #1 [ffff81024ad33980] rt_spin_lock_slowlock at ffffffff81286d15^M << Waiting
for inode_lock
 #2 [ffff81024ad33a40] __rt_spin_lock at ffffffff812873b0^M
 #3 [ffff81024ad33a50] rt_spin_lock at ffffffff812873bb^M
 #4 [ffff81024ad33a60] ifind_fast at ffffffff810c32a1^M
 #5 [ffff81024ad33a90] iget_locked at ffffffff810c3be8^M
 #6 [ffff81024ad33ad0] proc_get_inode at ffffffff810ebaff^M
 #7 [ffff81024ad33b10] proc_lookup at ffffffff810f082a^M
 #8 [ffff81024ad33b40] proc_root_lookup at ffffffff810ec312^M
 #9 [ffff81024ad33b70] do_lookup at ffffffff810b78f7^M
#10 [ffff81024ad33bc0] __link_path_walk at ffffffff810b9a93^M
#11 [ffff81024ad33c60] link_path_walk at ffffffff810b9fc1^M
#12 [ffff81024ad33d30] path_walk at ffffffff810ba073^M
#13 [ffff81024ad33d40] do_path_lookup at ffffffff810ba37a^M
#14 [ffff81024ad33d90] __path_lookup_intent_open at ffffffff810baeb0^M
#15 [ffff81024ad33de0] path_lookup_open at ffffffff810baf60^M
#16 [ffff81024ad33df0] open_namei at ffffffff810bb071^M
#17 [ffff81024ad33e80] do_filp_open at ffffffff810ae610^M
#18 [ffff81024ad33f30] do_sys_open at ffffffff810ae67f^M
#19 [ffff81024ad33f70] sys_open at ffffffff810ae729^M


PID: 16879  TASK: ffff81013a06a140  CPU: 3   COMMAND: "pdflush"^M
 #0 [ffff810023063aa0] schedule at ffffffff8128534c^M
 #1 [ffff810023063b58] rt_mutex_slowlock at ffffffff81286ac5^M  << Waiting for
Kernel Lock
 #2 [ffff810023063c28] rt_mutex_lock at ffffffff81285fb4^M
 #3 [ffff810023063c38] rt_down at ffffffff8105fec7^M
 #4 [ffff810023063c58] lock_kernel at ffffffff81287b8c^M
 #5 [ffff810023063c78] __blkdev_put at ffffffff810d5d31^M
 #6 [ffff810023063cb8] blkdev_put at ffffffff810d5e68^M
 #7 [ffff810023063cc8] close_dev at ffffffff8819e547^M
 #8 [ffff810023063ce8] dm_put_device at ffffffff8819e579^M
 #9 [ffff810023063d08] free_priority_group at ffffffff881c0e86^M
#10 [ffff810023063d58] free_multipath at ffffffff881c0f11^M
#11 [ffff810023063d78] multipath_dtr at ffffffff881c0f73^M
#12 [ffff810023063d98] dm_table_put at ffffffff8819e347^M
#13 [ffff810023063dc8] dm_any_congested at ffffffff8819d074^M
#14 [ffff810023063df8] sync_sb_inodes at ffffffff810cd451^M
#15 [ffff810023063e38] writeback_inodes at ffffffff810cd7b5^M
#16 [ffff810023063e68] background_writeout at ffffffff8108be38^M
#17 [ffff810023063ed8] pdflush at ffffffff8108c79a^M
#18 [ffff810023063f28] kthread at ffffffff81051477^M
#19 [ffff810023063f48] kernel_thread at ffffffff8100d048^M

crash> kernel_sem
kernel_sem = $5 = {
  count = {
    counter = 0
  }, 
  lock = {
    wait_lock = {
      raw_lock = {
        slock = 34952
      }, 
      break_lock = 0
    }, 
    wait_list = {
      prio_list = {
        next = 0xffff810023063b88, 
        prev = 0xffff81014941fdc0
      }, 
      node_list = {
        next = 0xffff810023063b98, 
        prev = 0xffff81014d04ddd0
      }
    }, 
    owner = 0xffff81024f03e102 << multipathd owns it. (task 0xffff81024f03e100) 
                                                   << last two bits are flags..
so replace it with 0.
  }
}
crash> inode_lock
inode_lock = $6 = {
  lock = {
    wait_lock = {
      raw_lock = {
        slock = 3341
      }, 
      break_lock = 0
    }, 
    wait_list = {
      prio_list = {
        next = 0xffff81024ad339a0, 
        prev = 0xffff8100784fdd78
      }, 
      node_list = {
        next = 0xffff81024ad339b0, 
        prev = 0xffff81024afb3a70
      }
    }, 
    owner = 0xffff81013a06a142 << pdflush owns it. (task 0xffff81013a06a140)
  }, 
  break_lock = 0
}
crash> 
----------------

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
----

Index: linux-2.6.28-rc3/drivers/md/dm.c
===================================================================
--- linux-2.6.28-rc3.orig/drivers/md/dm.c
+++ linux-2.6.28-rc3/drivers/md/dm.c
@@ -937,16 +937,21 @@ static void dm_unplug_all(struct request
 
 static int dm_any_congested(void *congested_data, int bdi_bits)
 {
-	int r;
+	int r = bdi_bits;
 	struct mapped_device *md = (struct mapped_device *) congested_data;
-	struct dm_table *map = dm_get_table(md);
+	struct dm_table *map;
 
-	if (!map || test_bit(DMF_BLOCK_IO, &md->flags))
-		r = bdi_bits;
-	else
-		r = dm_table_any_congested(map, bdi_bits);
+	atomic_inc(&md->pending);
+	if (test_bit(DMF_BLOCK_IO, &md->flags))
+		goto done;
 
-	dm_table_put(map);
+	map = dm_get_table(md);
+	if (map) {
+		r = dm_table_any_congested(map, bdi_bits);
+		dm_table_put(map);
+	}
+done:
+	atomic_dec(&md->pending);
 	return r;
 }