From: Ming Zhang Subject: Re: (un)lock_kernel() ? Date: Tue, 10 Apr 2007 12:03:15 -0400 Message-ID: <1176220995.3696.24.camel@fs0004.ibrix.com> References: <1175701002.6489.4.camel@shaggy> Reply-To: blackmagic02881@gmail.com Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Dave Kleikamp , linux-ext4@vger.kernel.org To: "John Anthony Kazos Jr." Return-path: Received: from wx-out-0506.google.com ([66.249.82.233]:56820 "EHLO wx-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030682AbXDJQDU (ORCPT ); Tue, 10 Apr 2007 12:03:20 -0400 Received: by wx-out-0506.google.com with SMTP id h31so1932360wxd for ; Tue, 10 Apr 2007 09:03:20 -0700 (PDT) In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, 2007-04-04 at 12:52 -0400, John Anthony Kazos Jr. wrote: > > According to Documentation/filesystems/Locking, ->get_sb() is called > > with the BKL held, but looking through the code, I'm not able to find > > where it is being taken. > > I noticed that too. Unless I'm just dumb and can't see it, I'm not able to > find any BKL references during filesystem mounting until you get into > FS-specific code. I looked through everything from sys_mount through to > vfs_kern_mount. Documentation/filesystems/porting talks about several > situations where the VFS code was modified to not take the BKL, and BLK > calls were added by FS non-maintainers for safety until each FS could be > audited independently, but that wouldn't be the case, would it? sys_mount->do_mount->do_new_mount->do_kern_mount path part of sys_mount() 1570 goto out3; 1571 1572 lock_kernel(); 1573 retval = do_mount((char *)dev_page, dir_page, (char *)type_page, 1574 flags, (void *)data_page); 1575 unlock_kernel(); 1576 free_page(data_page); 1577 1578 out3: 1579 free_page(dev_page) ; > > The ext2 code takes the BKL in three places: ext2_update_inode, > write_super, and ext2_compat_ioctl. Starting with ext3, it's in > ext3_compat_ioctl and ext3_fill_super, and the same with ext4. > > I suppose the BKL does have to be held, somehow, somewhere, during > mounting, or anybody using ext3 on a multiprocessor box would lock their > system from unmatched locking calls. Unless the first unlock_kernel() > would make the count -1 and the lock would bring it back to zero? > - > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html