Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

[Eric Ren <zren@suse.com>]

On 01/06/2017 02:09 PM, Joseph Qi wrote:
> Hi Eric,
>
>
> On 17/1/5 23:31, 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().
> As described cases above, shall we just add the tracking logic only for set/get_acl()?

The idea is to detect recursive locking on the running task stack. Take case 1) for example 
if ocfs2_permisssion()
is not changed:

ocfs2_permission() <=== take PR, ocfs2_holder is not added
    ocfs2_iop_get_acl <=== still take PR, because there is no lock holder on the tracking list

Thanks for your review;-)
Eric

>
> Thanks,
> Joseph
>>
>> Signed-off-by: Eric Ren <zren@suse.com>
>> ---
>>   fs/ocfs2/acl.c  | 39 ++++++++++++++++++++++++++++++++++-----
>>   fs/ocfs2/file.c | 44 ++++++++++++++++++++++++++++++++++----------
>>   2 files changed, 68 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
>> index bed1fcb..c539890 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_holder oh;
>> +    struct ocfs2_lock_res *lockres;
>> +
>> +    lockres = &OCFS2_I(inode)->ip_inode_lockres;
>> +    has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
>> +    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);
>> +
>>       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_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) != NULL);
>> +    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..62be75d 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_holder oh;
>> +    struct ocfs2_lock_res *lockres;
>>         trace_ocfs2_setattr(inode, dentry,
>>                   (unsigned long long)OCFS2_I(inode)->ip_blkno,
>> @@ -1173,13 +1176,20 @@ 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) != NULL);
>> +    if (had_lock)
>> +        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);
>>           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 +1270,8 @@ 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 +1289,10 @@ 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 +1334,31 @@ int ocfs2_getattr(struct vfsmount *mnt,
>>   int ocfs2_permission(struct inode *inode, int mask)
>>   {
>>       int ret;
>> +    int has_locked;
>> +    struct ocfs2_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) != NULL);
>> +    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);
>>       }
>>         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;
>>   }
>
>