From 4d885f90e3784df77945101d8ec32dc798a49862 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Mon, 13 Oct 2014 15:52:20 -0700 Subject: autofs4: avoid taking fs_lock during rcu-walk ->fs_lock protects AUTOFS_INF_EXPIRING. We need to be sure that once the flag is set, no new references beneath the dentry are taken. So rcu-walk currently needs to take fs_lock before checking the flag. This hurts performance. Change the expiry to a two-stage process. First set AUTOFS_INF_NO_RCU which forces any path walk into ref-walk mode, then drop the lock and call synchronize_rcu(). Once that returns we can be sure no rcu-walk is active beneath the dentry and we can check reference counts again. Now during an RCU-walk we can test AUTOFS_INF_EXPIRING without taking the lock as along as we test AUTOFS_INF_NO_RCU too. If either are set, we must abort the RCU-walk If neither are set, we know that refcounts will be tested again after we finish the RCU-walk so we are safe to continue. ->fs_lock is still taken in d_manage() to check for a non-trap directory. That will be resolved in the next patch. Signed-off-by: NeilBrown Reviewed-by: Ian Kent Tested-by: Ian Kent Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/autofs4/autofs_i.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs/autofs4/autofs_i.h') diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h index 2f1032f12d91..8e98cf954bab 100644 --- a/fs/autofs4/autofs_i.h +++ b/fs/autofs4/autofs_i.h @@ -79,6 +79,10 @@ struct autofs_info { }; #define AUTOFS_INF_EXPIRING (1<<0) /* dentry is in the process of expiring */ +#define AUTOFS_INF_NO_RCU (1<<1) /* the dentry is being considered + * for expiry, so RCU_walk is + * not permitted + */ #define AUTOFS_INF_PENDING (1<<2) /* dentry pending mount */ struct autofs_wait_queue { -- cgit v1.2.3