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Message-ID: <5a5b0ca7-d333-42e8-2e06-e209cb5c88a0@oracle.com>
Date: Mon, 16 Jan 2017 14:58:52 +0800
From: Junxiao Bi <junxiao.bi@...cle.com>
To: Eric Ren <zren@...e.com>, ocfs2-devel@....oracle.com
Cc: akpm@...ux-foundation.org, mfasheh@...sity.com, jlbec@...lplan.org,
ghe@...e.com, jiangqi903@...il.com, sfr@...b.auug.org.au,
hch@....de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] ocfs2: fix deadlock issue when taking inode lock
at vfs entry points
On 01/16/2017 02:42 PM, Eric Ren wrote:
> Commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()")
> results in a deadlock, as the author "Tariq Saeed" realized shortly
> after the patch was merged. The discussion happened here
> (https://oss.oracle.com/pipermail/ocfs2-devel/2015-September/011085.html).
>
> The reason why taking cluster inode lock at vfs entry points opens up
> a self deadlock window, is explained in the previous patch of this
> series.
>
> So far, we have seen two different code paths that have this issue.
> 1. do_sys_open
> may_open
> inode_permission
> ocfs2_permission
> ocfs2_inode_lock() <=== take PR
> generic_permission
> get_acl
> ocfs2_iop_get_acl
> ocfs2_inode_lock() <=== take PR
> 2. fchmod|fchmodat
> chmod_common
> notify_change
> ocfs2_setattr <=== take EX
> posix_acl_chmod
> get_acl
> ocfs2_iop_get_acl <=== take PR
> ocfs2_iop_set_acl <=== take EX
>
> Fixes them by adding the tracking logic (in the previous patch) for
> these funcs above, ocfs2_permission(), ocfs2_iop_[set|get]_acl(),
> ocfs2_setattr().
>
> Changes since v1:
> 1. Let ocfs2_is_locked_by_me() just return true/false to indicate if the
> process gets the cluster lock - suggested by: Joseph Qi <jiangqi903@...il.com>
> and Junxiao Bi <junxiao.bi@...cle.com>.
>
> 2. Change "struct ocfs2_holder" to a more meaningful name "ocfs2_lock_holder",
> suggested by: Junxiao Bi <junxiao.bi@...cle.com>.
>
> 3. Add debugging output at ocfs2_setattr() and ocfs2_permission() to
> catch exceptional cases, suggested by: Junxiao Bi <junxiao.bi@...cle.com>.
>
> Signed-off-by: Eric Ren <zren@...e.com>
> ---
> fs/ocfs2/acl.c | 39 +++++++++++++++++++++++++----
> fs/ocfs2/file.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 100 insertions(+), 15 deletions(-)
>
> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
> index bed1fcb..3e47262 100644
> --- a/fs/ocfs2/acl.c
> +++ b/fs/ocfs2/acl.c
> @@ -284,16 +284,31 @@ int ocfs2_iop_set_acl(struct inode *inode, struct posix_acl *acl, int type)
> {
> struct buffer_head *bh = NULL;
> int status = 0;
> -
> - status = ocfs2_inode_lock(inode, &bh, 1);
> + int arg_flags = 0, has_locked;
> + struct ocfs2_lock_holder oh;
> + struct ocfs2_lock_res *lockres;
> +
> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
> + has_locked = ocfs2_is_locked_by_me(lockres);
> + if (has_locked)
> + arg_flags = OCFS2_META_LOCK_GETBH;
> + status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
> if (status < 0) {
> if (status != -ENOENT)
> mlog_errno(status);
> return status;
> }
> + if (!has_locked)
> + ocfs2_add_holder(lockres, &oh);
> +
Same code pattern showed here and *get_acl, can it be abstracted to one
function?
The same issue for *setattr and *permission. Sorry for not mention that
in last review.
Thanks,
Junxiao.
> status = ocfs2_set_acl(NULL, inode, bh, type, acl, NULL, NULL);
> - ocfs2_inode_unlock(inode, 1);
> +
> + if (!has_locked) {
> + ocfs2_remove_holder(lockres, &oh);
> + ocfs2_inode_unlock(inode, 1);
> + }
> brelse(bh);
> +
> return status;
> }
>
> @@ -303,21 +318,35 @@ struct posix_acl *ocfs2_iop_get_acl(struct inode *inode, int type)
> struct buffer_head *di_bh = NULL;
> struct posix_acl *acl;
> int ret;
> + int arg_flags = 0, has_locked;
> + struct ocfs2_lock_holder oh;
> + struct ocfs2_lock_res *lockres;
>
> osb = OCFS2_SB(inode->i_sb);
> if (!(osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL))
> return NULL;
> - ret = ocfs2_inode_lock(inode, &di_bh, 0);
> +
> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
> + has_locked = ocfs2_is_locked_by_me(lockres);
> + if (has_locked)
> + arg_flags = OCFS2_META_LOCK_GETBH;
> + ret = ocfs2_inode_lock_full(inode, &di_bh, 0, arg_flags);
> if (ret < 0) {
> if (ret != -ENOENT)
> mlog_errno(ret);
> return ERR_PTR(ret);
> }
> + if (!has_locked)
> + ocfs2_add_holder(lockres, &oh);
>
> acl = ocfs2_get_acl_nolock(inode, type, di_bh);
>
> - ocfs2_inode_unlock(inode, 0);
> + if (!has_locked) {
> + ocfs2_remove_holder(lockres, &oh);
> + ocfs2_inode_unlock(inode, 0);
> + }
> brelse(di_bh);
> +
> return acl;
> }
>
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index c488965..b620c25 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -1138,6 +1138,9 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
> handle_t *handle = NULL;
> struct dquot *transfer_to[MAXQUOTAS] = { };
> int qtype;
> + int arg_flags = 0, had_lock;
> + struct ocfs2_lock_holder oh;
> + struct ocfs2_lock_res *lockres;
>
> trace_ocfs2_setattr(inode, dentry,
> (unsigned long long)OCFS2_I(inode)->ip_blkno,
> @@ -1173,13 +1176,41 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
> }
> }
>
> - status = ocfs2_inode_lock(inode, &bh, 1);
> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
> + had_lock = ocfs2_is_locked_by_me(lockres);
> + if (had_lock) {
> + arg_flags = OCFS2_META_LOCK_GETBH;
> +
> + /*
> + * As far as we know, ocfs2_setattr() could only be the first
> + * VFS entry point in the call chain of recursive cluster
> + * locking issue.
> + *
> + * For instance:
> + * chmod_common()
> + * notify_change()
> + * ocfs2_setattr()
> + * posix_acl_chmod()
> + * ocfs2_iop_get_acl()
> + *
> + * But, we're not 100% sure if it's always true, because the
> + * ordering of the VFS entry points in the call chain is out
> + * of our control. So, we'd better dump the stack here to
> + * catch the other cases of recursive locking.
> + */
> + mlog(ML_ERROR, "Another case of recursive locking:\n");
> + dump_stack();
> + }
> + status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
> if (status < 0) {
> if (status != -ENOENT)
> mlog_errno(status);
> goto bail_unlock_rw;
> }
> - inode_locked = 1;
> + if (!had_lock) {
> + ocfs2_add_holder(lockres, &oh);
> + inode_locked = 1;
> + }
>
> if (size_change) {
> status = inode_newsize_ok(inode, attr->ia_size);
> @@ -1260,7 +1291,8 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
> bail_commit:
> ocfs2_commit_trans(osb, handle);
> bail_unlock:
> - if (status) {
> + if (status && inode_locked) {
> + ocfs2_remove_holder(lockres, &oh);
> ocfs2_inode_unlock(inode, 1);
> inode_locked = 0;
> }
> @@ -1278,8 +1310,10 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
> if (status < 0)
> mlog_errno(status);
> }
> - if (inode_locked)
> + if (inode_locked) {
> + ocfs2_remove_holder(lockres, &oh);
> ocfs2_inode_unlock(inode, 1);
> + }
>
> brelse(bh);
> return status;
> @@ -1321,20 +1355,42 @@ int ocfs2_getattr(struct vfsmount *mnt,
> int ocfs2_permission(struct inode *inode, int mask)
> {
> int ret;
> + int has_locked;
> + struct ocfs2_lock_holder oh;
> + struct ocfs2_lock_res *lockres;
>
> if (mask & MAY_NOT_BLOCK)
> return -ECHILD;
>
> - ret = ocfs2_inode_lock(inode, NULL, 0);
> - if (ret) {
> - if (ret != -ENOENT)
> - mlog_errno(ret);
> - goto out;
> + lockres = &OCFS2_I(inode)->ip_inode_lockres;
> + has_locked = ocfs2_is_locked_by_me(lockres);
> + if (!has_locked) {
> + ret = ocfs2_inode_lock(inode, NULL, 0);
> + if (ret) {
> + if (ret != -ENOENT)
> + mlog_errno(ret);
> + goto out;
> + }
> + ocfs2_add_holder(lockres, &oh);
> + } else {
> + /* See comments in ocfs2_setattr() for details.
> + * The call chain of this case could be:
> + * do_sys_open()
> + * may_open()
> + * inode_permission()
> + * ocfs2_permission()
> + * ocfs2_iop_get_acl()
> + */
> + mlog(ML_ERROR, "Another case of recursive locking:\n");
> + dump_stack();
> }
>
> ret = generic_permission(inode, mask);
>
> - ocfs2_inode_unlock(inode, 0);
> + if (!has_locked) {
> + ocfs2_remove_holder(lockres, &oh);
> + ocfs2_inode_unlock(inode, 0);
> + }
> out:
> return ret;
> }
>
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