>From e2bd416f6246d11be29999c177d2534943a5c2df Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Thu, 27 Jun 2013 19:37:23 -0700
eb178d06332 ("cgroup: grab cgroup_mutex in
drop_parsed_module_refcounts()") made drop_parsed_module_refcounts()
grab cgroup_mutex to make lockdep assertion in for_each_subsys()
happy. Unfortunately, cgroup_remount() calls the function while
holding cgroup_mutex in its failure path leading to the following
deadlock.
# mount -t cgroup -o remount,memory,blkio cgroup blkio
cgroup: option changes via remount are deprecated (pid=525 comm=mount)
=============================================
[ INFO: possible recursive locking detected ]
3.10.0-rc4-work+ #1 Not tainted
---------------------------------------------
mount/525 is trying to acquire lock:
(cgroup_mutex){+.+.+.}, at: [<ffffffff8110a3e1>] drop_parsed_module_refcounts+0x21/0xb0
but task is already holding lock:
(cgroup_mutex){+.+.+.}, at: [<ffffffff8110e4e1>] cgroup_remount+0x51/0x200
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(cgroup_mutex);
lock(cgroup_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
4 locks held by mount/525:
#0: (&type->s_umount_key#30){+.+...}, at: [<ffffffff811e9a0d>] do_mount+0x2bd/0xa30
#1: (&sb->s_type->i_mutex_key#9){+.+.+.}, at: [<ffffffff8110e4d3>] cgroup_remount+0x43/0x200
#2: (cgroup_mutex){+.+.+.}, at: [<ffffffff8110e4e1>] cgroup_remount+0x51/0x200
#3: (cgroup_root_mutex){+.+.+.}, at: [<ffffffff8110e4ef>] cgroup_remount+0x5f/0x200
stack backtrace:
CPU: 2 PID: 525 Comm: mount Not tainted 3.10.0-rc4-work+ #1
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
ffffffff829651f0 ffff88000ec2fc28 ffffffff81c24bb1 ffff88000ec2fce8
ffffffff810f420d 0000000000000006 0000000000000001 0000000000000056
ffff8800153b4640 ffff880000000000 ffffffff81c2e468 ffff8800153b4640
Call Trace:
[<ffffffff81c24bb1>] dump_stack+0x19/0x1b
[<ffffffff810f420d>] __lock_acquire+0x15dd/0x1e60
[<ffffffff810f531c>] lock_acquire+0x9c/0x1f0
[<ffffffff81c2a805>] mutex_lock_nested+0x65/0x410
[<ffffffff8110a3e1>] drop_parsed_module_refcounts+0x21/0xb0
[<ffffffff8110e63e>] cgroup_remount+0x1ae/0x200
[<ffffffff811c9bb2>] do_remount_sb+0x82/0x190
[<ffffffff811e9d41>] do_mount+0x5f1/0xa30
[<ffffffff811ea203>] SyS_mount+0x83/0xc0
[<ffffffff81c2fb82>] system_call_fastpath+0x16/0x1b
Fix it by moving the drop_parsed_module_refcounts() invocation outside
cgroup_mutex.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
Two patches to fix regressions that I introduced lately. Given that
-rc1 is imminent, I applied them to for-3.11 directly so that they can
get exposure in -next ASAP.
Thanks!
kernel/cgroup.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4ed8677..1b7b567 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1365,7 +1365,6 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
if (opts.flags != root->flags ||
(opts.name && strcmp(opts.name, root->name))) {
ret = -EINVAL;
- drop_parsed_module_refcounts(opts.subsys_mask);
goto out_unlock;
}
@@ -1380,7 +1379,6 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
if (ret) {
/* rebind_subsystems failed, re-populate the removed files */
cgroup_populate_dir(cgrp, false, removed_mask);
- drop_parsed_module_refcounts(opts.subsys_mask);
goto out_unlock;
}
@@ -1395,6 +1393,8 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
mutex_unlock(&cgroup_root_mutex);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
+ if (ret)
+ drop_parsed_module_refcounts(opts.subsys_mask);
return ret;
}
--
1.8.3.1
_______________________________________________
Containers mailing list
Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/containers
