Re: [PATCH v3 2/2] ceph: wait the first reply of inflight async unlink

From: Xiubo Li <xiubli@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: jlayton@kernel.org, viro@zeniv.linux.org.uk, idryomov@gmail.com,
	vshankar@redhat.com, ceph-devel@vger.kernel.org,
	dchinner@redhat.com, hch@lst.de, arnd@arndb.de,
	mcgrof@kernel.org, akpm@linux-foundation.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	kernel test robot <lkp@intel.com>
Subject: Re: [PATCH v3 2/2] ceph: wait the first reply of inflight async unlink
Date: Wed, 18 May 2022 09:03:00 +0800	[thread overview]
Message-ID: <acf2457a-a984-d490-2833-be7cfd25c729@redhat.com> (raw)
In-Reply-To: <YoOy40sGQv4DjmAq@casper.infradead.org>

On 5/17/22 10:36 PM, Matthew Wilcox wrote:
> On Tue, May 17, 2022 at 08:55:49PM +0800, Xiubo Li wrote:
>> +int ceph_wait_on_conflict_unlink(struct dentry *dentry)
>> +{
>> +	struct ceph_fs_client *fsc = ceph_sb_to_client(dentry->d_sb);
>> +	struct dentry *pdentry = dentry->d_parent;
>> +	struct dentry *udentry, *found = NULL;
>> +	struct ceph_dentry_info *di;
>> +	struct qstr dname;
>> +	u32 hash = dentry->d_name.hash;
>> +	int err;
>> +
>> +	dname.name = dentry->d_name.name;
>> +	dname.len = dentry->d_name.len;
>> +
>> +	rcu_read_lock();
>> +	hash_for_each_possible_rcu(fsc->async_unlink_conflict, di,
>> +				   hnode, hash) {
>> +		udentry = di->dentry;
>> +
>> +		spin_lock(&udentry->d_lock);
>> +		if (udentry->d_name.hash != hash)
>> +			goto next;
>> +		if (unlikely(udentry->d_parent != pdentry))
>> +			goto next;
>> +		if (!hash_hashed(&di->hnode))
>> +			goto next;
>> +
>> +		if (!test_bit(CEPH_DENTRY_ASYNC_UNLINK_BIT, &di->flags))
>> +			pr_warn("%s dentry %p:%pd async unlink bit is not set\n",
>> +				__func__, dentry, dentry);
>> +
>> +		if (d_compare(pdentry, udentry, &dname))
>> +			goto next;
>> +
>> +		spin_unlock(&udentry->d_lock);
>> +		found = dget(udentry);
>> +		break;
>> +next:
>> +		spin_unlock(&udentry->d_lock);
>> +	}
>> +	rcu_read_unlock();
>> +
>> +	if (likely(!found))
>> +		return 0;
>> +
>> +	dout("%s dentry %p:%pd conflict with old %p:%pd\n", __func__,
>> +	     dentry, dentry, found, found);
>> +
>> +	err = wait_on_bit(&di->flags, CEPH_DENTRY_ASYNC_UNLINK_BIT,
>> +			  TASK_INTERRUPTIBLE);
> Do you really want to use TASK_INTERRUPTIBLE here?  If the window is
> resized and you get a SIGWINCH, or a timer goes off and you get a
> SIGALRM, you want to return -EINTR?  I would suggest that TASK_KILLABLE
> is probably the semantics that you want.
>
Sounds reasonable.  I will switch to use the TASK_KILLABLE.

@Jeff

I just copied this code from ceph_wait_on_async_create(). BTW, do we 
have any other consideration that we must use the TASK_INTERRUPTIBLE there ?

Thanks.

-- Xiubo