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Message-ID: <f983a441-68b9-c793-c7e6-30ad02c40136@suse.com>
Date: Fri, 6 Jan 2017 19:56:13 +0800
From: Eric Ren <zren@...e.com>
To: Joseph Qi <jiangqi903@...il.com>, ocfs2-devel@....oracle.com
Cc: akpm@...ux-foundation.org, mfasheh@...sity.com, jlbec@...lplan.org,
ghe@...e.com, junxiao.bi@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs
entry points
Hi!
On 01/06/2017 05:55 PM, Joseph Qi wrote:
> On 17/1/6 17:13, Eric Ren wrote:
>> Hi,
>>
>>>>>>>>
>>>>>>>> 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
>>>>> I mean we have no need to check if locked by me, just do inode lock and add holder.
>>>>> This will make code more clean, IMO.
>>>> Oh, sorry, I get your point this time. I think we need to check it if there are more
>>>> than one processes that hold
>>>> PR lock on the same resource. If I don't understand you correctly, please tell me why
>>>> you think it's not neccessary
>>>> to check before getting lock?
>>> The code logic can only check if it is locked by myself. In the case
>> Why only...?
>>> described above, ocfs2_permission is the first entry to take inode lock.
>>> And even if check succeeds, it is a bug without unlock, but not the case
>>> of recursive lock.
>>
>> By checking succeeds, you mean it's locked by me, right? If so, this flag
>> "arg_flags = OCFS2_META_LOCK_GETBH"
>> will be passed down to ocfs2_inode_lock_full(), which gets back buffer head of
>> the disk inode for us if necessary, but doesn't take cluster locking again. So, there is
>> no need to unlock in such case.
> I am trying to state my point more clearly...
Thanks a lot!
> The issue case you are trying to fix is:
> Process A
> take inode lock (phase1)
> ...
> <<< race window (phase2, Process B)
The deadlock only happens if process B is on a remote node and request EX lock.
Quote the patch[1/2]'s commit message:
A deadlock will occur if a remote EX request comes in between two of
ocfs2_inode_lock(). Briefly describe how the deadlock is formed:
On one hand, OCFS2_LOCK_BLOCKED flag of this lockres is set in
BAST(ocfs2_generic_handle_bast) when downconvert is started on behalf of
the remote EX lock request. Another hand, the recursive cluster lock (the
second one) will be blocked in in __ocfs2_cluster_lock() because of
OCFS2_LOCK_BLOCKED. But, the downconvert never complete, why? because
there is no chance for the first cluster lock on this node to be unlocked
- we block ourselves in the code path.
---
> ...
> take inode lock again (phase3)
>
> Deadlock happens because Process B in phase2 and Process A in phase3
> are waiting for each other.
It's local lock's (like i_mutex) responsibility to protect critical section from racing
among processes on the same node.
> So you are trying to fix it by making phase3 finish without really doing
Phase3 can go ahead because this node is already under protection of cluster lock.
> __ocfs2_cluster_lock, then Process B can continue either.
> Let us bear in mind that phase1 and phase3 are in the same context and
> executed in order. That's why I think there is no need to check if locked
> by myself in phase1.
> If phase1 finds it is already locked by myself, that means the holder
> is left by last operation without dec holder. That's why I think it is a bug
> instead of a recursive lock case.
Did I answer your question?
Thanks!
Eric
>
> Thanks,
> Joseph
>>
>> Thanks,
>> Eric
>>
>>>
>>> Thanks,
>>> Joseph
>>>>
>>>> Thanks,
>>>> Eric
>>>>>
>>>>> Thanks,
>>>>> Joseph
>>>>>>
>>>>>> Thanks for your review;-)
>>>>>> Eric
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Joseph
>>>>>>>>
>>>>>>>> Signed-off-by: Eric Ren <zren@...e.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;
>>>>>>>> }
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>
>
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