From: Li Zefan Date: Tue, 15 Jan 2013 06:10:57 +0000 (+0800) Subject: cpuset: fix RCU lockdep splat X-Git-Tag: v3.9-rc1~156^2~1 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=27e89ae5d6e94e30231ee89a7736f62d84ba4c6f;p=pandora-kernel.git cpuset: fix RCU lockdep splat 5d21cc2db040d01f8c19b8602f6987813e1176b4 ("cpuset: replace cgroup_mutex locking with cpuset internal locking") incorrectly converted proc_cpuset_show() from cgroup_lock() to cpuset_mutex. proc_cpuset_show() is accessing cgroup hierarchy proper to determine cgroup path which can't be protected by cpuset_mutex. This triggered the following RCU warning. =============================== [ INFO: suspicious RCU usage. ] 3.8.0-rc3-next-20130114-sasha-00016-ga107525-dirty #262 Tainted: G W ------------------------------- include/linux/cgroup.h:534 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 2 locks held by trinity/7514: #0: (&p->lock){+.+.+.}, at: [] seq_read+0x3a/0x3e0 #1: (cpuset_mutex){+.+...}, at: [] proc_cpuset_show+0x84/0x190 stack backtrace: Pid: 7514, comm: trinity Tainted: G W +3.8.0-rc3-next-20130114-sasha-00016-ga107525-dirty #262 Call Trace: [] lockdep_rcu_suspicious+0x10b/0x120 [] proc_cpuset_show+0x111/0x190 [] seq_read+0x1b7/0x3e0 [] ? seq_lseek+0x110/0x110 [] do_loop_readv_writev+0x4b/0x90 [] do_readv_writev+0xf6/0x1d0 [] vfs_readv+0x3e/0x60 [] sys_readv+0x50/0xd0 [] tracesys+0xe1/0xe6 The operation can be performed under RCU read lock. Replace cpuset_mutex locking with RCU read locking. tj: Rewrote patch description. Reported-by: Sasha Levin Signed-off-by: Li Zefan Signed-off-by: Tejun Heo --- Reading git-diff-tree failed