[Ocfs2-devel] [PATCH] ocfs2: fix a potential 'ABBA' deadlock caused by 'l_lock' and 'dentry_attach_lock'
piaojun
piaojun at huawei.com
Thu Dec 7 04:36:42 PST 2017
Hi Changwei,
On 2017/12/7 19:59, Changwei Ge wrote:
> Hi Jun,
>
> On 2017/12/7 19:30, piaojun wrote:
>> CPUA CPUB
>>
>> ocfs2_dentry_convert_worker
>> get 'l_lock'
>
> This lock belongs to ocfs2_dentry_lock::ocfs2_lock_res::l_lock
>
>>
>> get 'dentry_attach_lock'
>>
>> interruptted by dio_end_io:
>> dio_end_io
>> dio_bio_end_aio
>> dio_complete
>> dio->end_io
>> ocfs2_dio_end_io
>> ocfs2_rw_unlock
>> ...
>> try to get 'l_lock'
>
> This lock belongs to ocfs2_lock_res::l_lock though.
>
> So I think they are totally two different locks.
> So making spin_lock to interruption safe is pointless.
>
> Thanks,
> Changwei
>
For the same lock, we need use spin_lock_irqsave to ensure irq-safe as
you said. But the scenario described above is another kind of deadlock
caused by two different locks which stuck each other. To avoid this
'ABBA' deadlock we need follow the rule that 'spin_lock_irqsave' should
be called under 'spin_lock_irqsave'.
thanks,
Jun
>> but CPUA has got it.
>>
>> try to get 'dentry_attach_lock',
>> but CPUB has got 'dentry_attach_lock',
>> and would not release it.
>>
>> so we need use spin_lock_irqsave for 'dentry_attach_lock' to prevent
>> interruptted by softirq.
>>
>> Signed-off-by: Jun Piao <piaojun at huawei.com>
>> Reviewed-by: Alex Chen <alex.chen at huawei.com>
>> ---
>> fs/ocfs2/dcache.c | 14 ++++++++------
>> fs/ocfs2/dlmglue.c | 14 +++++++-------
>> fs/ocfs2/namei.c | 5 +++--
>> 3 files changed, 18 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/ocfs2/dcache.c b/fs/ocfs2/dcache.c
>> index 2903730..6555fbf 100644
>> --- a/fs/ocfs2/dcache.c
>> +++ b/fs/ocfs2/dcache.c
>> @@ -230,6 +230,7 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
>> int ret;
>> struct dentry *alias;
>> struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
>> + unsigned long flags;
>>
>> trace_ocfs2_dentry_attach_lock(dentry->d_name.len, dentry->d_name.name,
>> (unsigned long long)parent_blkno, dl);
>> @@ -309,10 +310,10 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
>> ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);
>>
>> out_attach:
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, flags);
>> dentry->d_fsdata = dl;
>> dl->dl_count++;
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, flags);
>>
>> /*
>> * This actually gets us our PRMODE level lock. From now on,
>> @@ -333,9 +334,9 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
>> if (ret < 0 && !alias) {
>> ocfs2_lock_res_free(&dl->dl_lockres);
>> BUG_ON(dl->dl_count != 1);
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, flags);
>> dentry->d_fsdata = NULL;
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, flags);
>> kfree(dl);
>> iput(inode);
>> }
>> @@ -379,13 +380,14 @@ void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
>> struct ocfs2_dentry_lock *dl)
>> {
>> int unlock = 0;
>> + unsigned long flags;
>>
>> BUG_ON(dl->dl_count == 0);
>>
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, flags);
>> dl->dl_count--;
>> unlock = !dl->dl_count;
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, flags);
>>
>> if (unlock)
>> ocfs2_drop_dentry_lock(osb, dl);
>> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
>> index 4689940..9bff3d2 100644
>> --- a/fs/ocfs2/dlmglue.c
>> +++ b/fs/ocfs2/dlmglue.c
>> @@ -3801,7 +3801,7 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
>> struct ocfs2_dentry_lock *dl = ocfs2_lock_res_dl(lockres);
>> struct ocfs2_inode_info *oi = OCFS2_I(dl->dl_inode);
>> struct dentry *dentry;
>> - unsigned long flags;
>> + unsigned long flags, d_flags;
>> int extra_ref = 0;
>>
>> /*
>> @@ -3831,13 +3831,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
>> * flag.
>> */
>> spin_lock_irqsave(&lockres->l_lock, flags);
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, d_flags);
>> if (!(lockres->l_flags & OCFS2_LOCK_FREEING)
>> && dl->dl_count) {
>> dl->dl_count++;
>> extra_ref = 1;
>> }
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
>> spin_unlock_irqrestore(&lockres->l_lock, flags);
>>
>> mlog(0, "extra_ref = %d\n", extra_ref);
>> @@ -3850,13 +3850,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
>> if (!extra_ref)
>> return UNBLOCK_CONTINUE;
>>
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, d_flags);
>> while (1) {
>> dentry = ocfs2_find_local_alias(dl->dl_inode,
>> dl->dl_parent_blkno, 1);
>> if (!dentry)
>> break;
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
>>
>> if (S_ISDIR(dl->dl_inode->i_mode))
>> shrink_dcache_parent(dentry);
>> @@ -3874,9 +3874,9 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
>> d_delete(dentry);
>> dput(dentry);
>>
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, d_flags);
>> }
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
>>
>> /*
>> * If we are the last holder of this dentry lock, there is no
>> diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
>> index 3b0a10d..a17454e 100644
>> --- a/fs/ocfs2/namei.c
>> +++ b/fs/ocfs2/namei.c
>> @@ -223,13 +223,14 @@ static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb,
>> struct dentry *dentry, struct inode *inode)
>> {
>> struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
>> + unsigned long flags;
>>
>> ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);
>> ocfs2_lock_res_free(&dl->dl_lockres);
>> BUG_ON(dl->dl_count != 1);
>> - spin_lock(&dentry_attach_lock);
>> + spin_lock_irqsave(&dentry_attach_lock, flags);
>> dentry->d_fsdata = NULL;
>> - spin_unlock(&dentry_attach_lock);
>> + spin_unlock_irqrestore(&dentry_attach_lock, flags);
>> kfree(dl);
>> iput(inode);
>> }
>>
>
> .
>
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