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Date:   Mon, 16 Jan 2017 15:35:12 +0800
From:   Eric Ren <zren@...e.com>
To:     Junxiao Bi <junxiao.bi@...cle.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

Hi!

On 01/16/2017 02:58 PM, Junxiao Bi wrote:
> 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.

Good idea! I will do it in the next version;-)

Thanks,
Eric

>
> 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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