Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762595AbXKAXS1 (ORCPT ); Thu, 1 Nov 2007 19:18:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760187AbXKAXJP (ORCPT ); Thu, 1 Nov 2007 19:09:15 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:38639 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755154AbXKAXJG (ORCPT ); Thu, 1 Nov 2007 19:09:06 -0400 Subject: [PATCH 27/27] keep track of mnt_writer state of struct file To: akpm@osdl.org Cc: linux-kernel@vger.kernel.org, miklos@szeredi.hu, hch@infradead.org, Dave Hansen From: Dave Hansen Date: Thu, 01 Nov 2007 16:09:02 -0700 References: <20071101230826.9A4F6E00@kernel> In-Reply-To: <20071101230826.9A4F6E00@kernel> Message-Id: <20071101230902.F256608C@kernel> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4407 Lines: 126 There have been a few oopses caused by 'struct file's with NULL f_vfsmnts. There was also a set of potentially missed mnt_want_write()s from dentry_open() calls. This patch provides a very simple debugging framework to catch these kinds of bugs. It will WARN_ON() them, but should stop us from having any oopses or mnt_writer count imbalances. I'm quite convinced that this is a good thing because it found bugs in the stuff I was working on as soon as I wrote it. Signed-off-by: Dave Hansen --- linux-2.6.git-dave/fs/file_table.c | 21 +++++++++++++++++++-- linux-2.6.git-dave/fs/open.c | 14 +++++++++++++- linux-2.6.git-dave/include/linux/fs.h | 4 ++++ 3 files changed, 36 insertions(+), 3 deletions(-) diff -puN fs/file_table.c~keep-track-of-mnt_writer-state-of-struct-file fs/file_table.c --- linux-2.6.git/fs/file_table.c~keep-track-of-mnt_writer-state-of-struct-file 2007-11-01 14:46:22.000000000 -0700 +++ linux-2.6.git-dave/fs/file_table.c 2007-11-01 14:46:22.000000000 -0700 @@ -42,6 +42,12 @@ static inline void file_free_rcu(struct static inline void file_free(struct file *f) { percpu_counter_dec(&nr_files); + /* + * At this point, either both or neither of these bits + * should be set. + */ + WARN_ON(f->f_mnt_write_state == FILE_MNT_WRITE_TAKEN); + WARN_ON(f->f_mnt_write_state == FILE_MNT_WRITE_RELEASED); call_rcu(&f->f_u.fu_rcuhead, file_free_rcu); } @@ -201,6 +207,7 @@ int init_file(struct file *file, struct * that we can do debugging checks at __fput()e */ if ((mode & FMODE_WRITE) && !special_file(dentry->d_inode->i_mode)) { + file->f_mnt_write_state = FILE_MNT_WRITE_TAKEN; error = mnt_want_write(mnt); WARN_ON(error); } @@ -243,8 +250,18 @@ void fastcall __fput(struct file *file) fops_put(file->f_op); if (file->f_mode & FMODE_WRITE) { put_write_access(inode); - if (!special_file(inode->i_mode)) - mnt_drop_write(mnt); + if (!special_file(inode->i_mode)) { + if (file->f_mnt_write_state == FILE_MNT_WRITE_TAKEN) { + mnt_drop_write(mnt); + file->f_mnt_write_state |= + FILE_MNT_WRITE_RELEASED; + } else { + printk(KERN_WARNING "__fput() of writeable " + "file with no " + "mnt_want_write()\n"); + WARN_ON(1); + } + } } put_pid(file->f_owner.pid); file_kill(file); diff -puN fs/open.c~keep-track-of-mnt_writer-state-of-struct-file fs/open.c --- linux-2.6.git/fs/open.c~keep-track-of-mnt_writer-state-of-struct-file 2007-11-01 14:46:22.000000000 -0700 +++ linux-2.6.git-dave/fs/open.c 2007-11-01 14:46:22.000000000 -0700 @@ -810,6 +810,10 @@ static struct file *__dentry_open(struct error = __get_file_write_access(inode, mnt); if (error) goto cleanup_file; + if (!special_file(inode->i_mode)) { + WARN_ON(f->f_mnt_write_state != 0); + f->f_mnt_write_state = FILE_MNT_WRITE_TAKEN; + } } f->f_mapping = inode->i_mapping; @@ -851,8 +855,16 @@ cleanup_all: fops_put(f->f_op); if (f->f_mode & FMODE_WRITE) { put_write_access(inode); - if (!special_file(inode->i_mode)) + if (!special_file(inode->i_mode)) { + /* + * We don't consider this a real + * mnt_want/drop_write() pair + * because it all happenend right + * here, so just reset the state. + */ + f->f_mnt_write_state = 0; mnt_drop_write(mnt); + } } file_kill(f); f->f_path.dentry = NULL; diff -puN include/linux/fs.h~keep-track-of-mnt_writer-state-of-struct-file include/linux/fs.h --- linux-2.6.git/include/linux/fs.h~keep-track-of-mnt_writer-state-of-struct-file 2007-11-01 14:46:22.000000000 -0700 +++ linux-2.6.git-dave/include/linux/fs.h 2007-11-01 14:46:22.000000000 -0700 @@ -774,6 +774,9 @@ static inline int ra_has_index(struct fi index < ra->start + ra->size); } +#define FILE_MNT_WRITE_TAKEN 1 +#define FILE_MNT_WRITE_RELEASED 2 + struct file { /* * fu_list becomes invalid after file_free is called and queued via @@ -808,6 +811,7 @@ struct file { spinlock_t f_ep_lock; #endif /* #ifdef CONFIG_EPOLL */ struct address_space *f_mapping; + unsigned long f_mnt_write_state; }; extern spinlock_t files_lock; #define file_list_lock() spin_lock(&files_lock); _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/