From: Dave Hansen With the r/o bind mount patches, we can have as many spinlocks nested as there are CPUs on the system. Lockdep freaks out after 8. So, create a new lockdep class of locks for the mnt_writer spinlocks, and initialize each of the cpu locks to be in a different class. It should shut up warnings like this, while still allowing some of the lockdep goodness to remain: ============================================= [ INFO: possible recursive locking detected ] 2.6.23-rc6 #6 --------------------------------------------- swapper/1 is trying to acquire lock: (&writer->lock){--..}, at: [] lock_and_coalesce_cpu_mnt_writer_counts+0x29/0x5c but task is already holding lock: (&writer->lock){--..}, at: [] lock_and_coalesce_cpu_mnt_writer_counts+0x29/0x5c other info that might help us debug this: 1 lock held by swapper/1: #0: (&writer->lock){--..}, at: [] lock_and_coalesce_cpu_mnt_writer_counts+0x29/0x5c stack backtrace: [] show_trace_log_lvl+0x19/0x2e [] show_trace+0x12/0x14 [] dump_stack+0x14/0x16 [] print_deadlock_bug+0xb7/0xc1 [] check_deadlock+0x40/0x54 [] validate_chain+0x26e/0x319 [] __lock_acquire+0x6c4/0x731 [] lock_acquire+0x7a/0x94 [] _spin_lock+0x38/0x62 [] lock_and_coalesce_cpu_mnt_writer_counts+0x29/0x5c [] mntput_no_expire+0x38/0xad [] path_release_on_umount+0x15/0x18 [] sys_umount+0x67/0x6f [] name_to_dev_t+0x22a/0x24c [] prepare_namespace+0x89/0x187 [] kernel_init+0x9a/0xa3 [] kernel_thread_helper+0x7/0x10 ======================= Signed-off-by: Dave Hansen Acked-by: Peter Zijlstra Signed-off-by: Andrew Morton --- fs/namespace.c | 2 ++ 1 files changed, 2 insertions(+) diff -puN fs/namespace.c~r-o-bind-mounts-track-number-of-mount-writers-make-lockdep-happy-with-r-o-bind-mounts fs/namespace.c --- a/fs/namespace.c~r-o-bind-mounts-track-number-of-mount-writers-make-lockdep-happy-with-r-o-bind-mounts +++ a/fs/namespace.c @@ -115,6 +115,7 @@ struct mnt_writer { * must be ordered by cpu number. */ spinlock_t lock; + struct lock_class_key lock_class; /* compiles out with !lockdep */ unsigned long count; struct vfsmount *mnt; } ____cacheline_aligned_in_smp; @@ -126,6 +127,7 @@ static int __init init_mnt_writers(void) for_each_possible_cpu(cpu) { struct mnt_writer *writer = &per_cpu(mnt_writers, cpu); spin_lock_init(&writer->lock); + lockdep_set_class(&writer->lock, &writer->lock_class); writer->count = 0; } return 0; _