From: NeilBrown Date: Mon, 13 Oct 2014 22:52:20 +0000 (-0700) Subject: autofs4: avoid taking fs_lock during rcu-walk X-Git-Tag: fixes-against-v3.18-rc2~79^2~96 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4d885f90e3784df77945101d8ec32dc798a49862;p=pandora-kernel.git 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 --- Reading git-diff-tree failed