Re: [PATCH 1/5] ceph: keep auth cap when inode has flocks or posix locks

[Jeff Layton <jlayton@redhat.com>]

On Tue, 2017-09-12 at 21:36 +0800, Yan, Zheng wrote:
> > On 12 Sep 2017, at 21:21, Jeff Layton <jlayton@redhat.com> wrote:
> > 
> > On Tue, 2017-09-12 at 10:53 +0800, Yan, Zheng wrote:
> > > file locks are tracked by inode's auth mds. releasing auth caps
> > > is equivalent to releasing all file locks.
> > > 
> > > Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
> > > ---
> > > fs/ceph/inode.c      |  1 +
> > > fs/ceph/locks.c      | 62 ++++++++++++++++++++++++++++++++++++++++++++--------
> > > fs/ceph/mds_client.c |  2 ++
> > > fs/ceph/super.h      |  1 +
> > > 4 files changed, 57 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
> > > index 373dab5173ca..c70b26d2bf8a 100644
> > > --- a/fs/ceph/inode.c
> > > +++ b/fs/ceph/inode.c
> > > @@ -492,6 +492,7 @@ struct inode *ceph_alloc_inode(struct super_block *sb)
> > > 	ci->i_wb_ref = 0;
> > > 	ci->i_wrbuffer_ref = 0;
> > > 	ci->i_wrbuffer_ref_head = 0;
> > > +	atomic_set(&ci->i_filelock_ref, 0);
> > > 	ci->i_shared_gen = 0;
> > > 	ci->i_rdcache_gen = 0;
> > > 	ci->i_rdcache_revoking = 0;
> > > diff --git a/fs/ceph/locks.c b/fs/ceph/locks.c
> > > index 64ae74472046..69f731e75302 100644
> > > --- a/fs/ceph/locks.c
> > > +++ b/fs/ceph/locks.c
> > > @@ -29,19 +29,46 @@ void __init ceph_flock_init(void)
> > > 	get_random_bytes(&lock_secret, sizeof(lock_secret));
> > > }
> > > 
> > > +static void ceph_fl_copy_lock(struct file_lock *dst, struct file_lock *src)
> > > +{
> > > +	struct inode *inode = file_inode(src->fl_file);
> > > +	atomic_inc(&ceph_inode(inode)->i_filelock_ref);
> > > +}
> > > +
> > > +static void ceph_fl_release_lock(struct file_lock *fl)
> > > +{
> > > +	struct inode *inode = file_inode(fl->fl_file);
> > > +	atomic_dec(&ceph_inode(inode)->i_filelock_ref);
> > > +}
> > > +
> > > +static const struct file_lock_operations ceph_fl_lock_ops = {
> > > +	.fl_copy_lock = ceph_fl_copy_lock,
> > > +	.fl_release_private = ceph_fl_release_lock,
> > > +};
> > > +
> > > /**
> > >  * Implement fcntl and flock locking functions.
> > >  */
> > > -static int ceph_lock_message(u8 lock_type, u16 operation, struct file *file,
> > > +static int ceph_lock_message(u8 lock_type, u16 operation, struct inode *inode,
> > > 			     int cmd, u8 wait, struct file_lock *fl)
> > > {
> > > -	struct inode *inode = file_inode(file);
> > > 	struct ceph_mds_client *mdsc = ceph_sb_to_client(inode->i_sb)->mdsc;
> > > 	struct ceph_mds_request *req;
> > > 	int err;
> > > 	u64 length = 0;
> > > 	u64 owner;
> > > 
> > > +	if (operation == CEPH_MDS_OP_SETFILELOCK) {
> > > +		/*
> > > +		 * increasing i_filelock_ref closes race window between
> > > +		 * handling request reply and adding file_lock struct to
> > > +		 * inode. Otherwise, i_auth_cap may get trimmed in the
> > > +		 * window. Caller function will decrease the counter.
> > > +		 */
> > > +		fl->fl_ops = &ceph_fl_lock_ops;
> > > +		atomic_inc(&ceph_inode(inode)->i_filelock_ref);
> > > +	}
> > > +
> > > 	if (operation != CEPH_MDS_OP_SETFILELOCK || cmd == CEPH_LOCK_UNLOCK)
> > > 		wait = 0;
> > > 
> > > @@ -179,10 +206,11 @@ static int ceph_lock_wait_for_completion(struct ceph_mds_client *mdsc,
> > >  */
> > > int ceph_lock(struct file *file, int cmd, struct file_lock *fl)
> > > {
> > > -	u8 lock_cmd;
> > > +	struct inode *inode = file_inode(file);
> > > 	int err;
> > > -	u8 wait = 0;
> > > 	u16 op = CEPH_MDS_OP_SETFILELOCK;
> > > +	u8 lock_cmd;
> > > +	u8 wait = 0;
> > > 
> > > 	if (!(fl->fl_flags & FL_POSIX))
> > > 		return -ENOLCK;
> > > @@ -198,6 +226,17 @@ int ceph_lock(struct file *file, int cmd, struct file_lock *fl)
> > > 	else if (IS_SETLKW(cmd))
> > > 		wait = 1;
> > > 
> > > +	if (op == CEPH_MDS_OP_SETFILELOCK) {
> > > +		/*
> > > +		 * increasing i_filelock_ref closes race window between
> > > +		 * handling request reply and adding file_lock struct to
> > > +		 * inode. Otherwise, i_auth_cap may get trimmed in the
> > > +		 * window. Caller function will decrease the counter.
> > > +		 */
> > > +		fl->fl_ops = &ceph_fl_lock_ops;
> > > +		atomic_inc(&ceph_inode(inode)->i_filelock_ref);
> > > +	}
> > > +
> > > 	if (F_RDLCK == fl->fl_type)
> > > 		lock_cmd = CEPH_LOCK_SHARED;
> > > 	else if (F_WRLCK == fl->fl_type)
> > > @@ -205,7 +244,7 @@ int ceph_lock(struct file *file, int cmd, struct file_lock *fl)
> > > 	else
> > > 		lock_cmd = CEPH_LOCK_UNLOCK;
> > > 
> > > -	err = ceph_lock_message(CEPH_LOCK_FCNTL, op, file, lock_cmd, wait, fl);
> > > +	err = ceph_lock_message(CEPH_LOCK_FCNTL, op, inode, lock_cmd, wait, fl);
> > > 	if (!err) {
> > > 		if (op != CEPH_MDS_OP_GETFILELOCK) {
> > > 			dout("mds locked, locking locally");
> > > @@ -214,7 +253,7 @@ int ceph_lock(struct file *file, int cmd, struct file_lock *fl)
> > > 				/* undo! This should only happen if
> > > 				 * the kernel detects local
> > > 				 * deadlock. */
> > > -				ceph_lock_message(CEPH_LOCK_FCNTL, op, file,
> > > +				ceph_lock_message(CEPH_LOCK_FCNTL, op, inode,
> > > 						  CEPH_LOCK_UNLOCK, 0, fl);
> > > 				dout("got %d on posix_lock_file, undid lock",
> > > 				     err);
> > > @@ -226,8 +265,9 @@ int ceph_lock(struct file *file, int cmd, struct file_lock *fl)
> > > 
> > > int ceph_flock(struct file *file, int cmd, struct file_lock *fl)
> > > {
> > > -	u8 lock_cmd;
> > > +	struct inode *inode = file_inode(file);
> > > 	int err;
> > > +	u8 lock_cmd;
> > > 	u8 wait = 0;
> > > 
> > > 	if (!(fl->fl_flags & FL_FLOCK))
> > > @@ -238,6 +278,10 @@ int ceph_flock(struct file *file, int cmd, struct file_lock *fl)
> > > 
> > > 	dout("ceph_flock, fl_file: %p", fl->fl_file);
> > > 
> > > +	/* see comment in ceph_lock */
> > > +	fl->fl_ops = &ceph_fl_lock_ops;
> > > +	atomic_inc(&ceph_inode(inode)->i_filelock_ref);
> > > +
> > > 	if (IS_SETLKW(cmd))
> > > 		wait = 1;
> > > 
> > > @@ -249,13 +293,13 @@ int ceph_flock(struct file *file, int cmd, struct file_lock *fl)
> > > 		lock_cmd = CEPH_LOCK_UNLOCK;
> > > 
> > > 	err = ceph_lock_message(CEPH_LOCK_FLOCK, CEPH_MDS_OP_SETFILELOCK,
> > > -				file, lock_cmd, wait, fl);
> > > +				inode, lock_cmd, wait, fl);
> > > 	if (!err) {
> > > 		err = locks_lock_file_wait(file, fl);
> > > 		if (err) {
> > > 			ceph_lock_message(CEPH_LOCK_FLOCK,
> > > 					  CEPH_MDS_OP_SETFILELOCK,
> > > -					  file, CEPH_LOCK_UNLOCK, 0, fl);
> > > +					  inode, CEPH_LOCK_UNLOCK, 0, fl);
> > > 			dout("got %d on locks_lock_file_wait, undid lock", err);
> > > 		}
> > > 	}
> > > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> > > index 9dd6b836ac9e..6146af4ed03c 100644
> > > --- a/fs/ceph/mds_client.c
> > > +++ b/fs/ceph/mds_client.c
> > > @@ -1461,6 +1461,8 @@ static int trim_caps_cb(struct inode *inode, struct ceph_cap *cap, void *arg)
> > > 			goto out;
> > > 		if ((used | wanted) & CEPH_CAP_ANY_WR)
> > > 			goto out;
> > > +		if (atomic_read(&ci->i_filelock_ref) > 0)
> > > +			goto out;
> > 
> > Is there a potential race here? Could i_filelock_ref do a 0->1
> > transition just after you check it?
> 
> It’s possible, but it does not hurt. Because i_filelock_ref gets increased before sending mds request.
> The extra reference gets dropped after setup the kernel file_lock data structure. The reply of mds
> request re-add auth cap if auth caps was dropped.
> 
> Regards
> Yan, Zheng
> 

Hmm, ok. It'd be nice to flesh out the description a bit, and talk about
 what problem this fixes. I guess this is just a best effort thing to
avoid releasing auth caps if locks are held or are being requested? It's
not immediately obvious to me.

With that understood, the patch itself looks ok:

Acked-by: Jeff Layton <jlayton@redhat.com>

> > 
> > > 	}
> > > 	/* The inode has cached pages, but it's no longer used.
> > > 	 * we can safely drop it */
> > > diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> > > index 279a2f401cf5..9e0de8264257 100644
> > > --- a/fs/ceph/super.h
> > > +++ b/fs/ceph/super.h
> > > @@ -351,6 +351,7 @@ struct ceph_inode_info {
> > > 	int i_pin_ref;
> > > 	int i_rd_ref, i_rdcache_ref, i_wr_ref, i_wb_ref;
> > > 	int i_wrbuffer_ref, i_wrbuffer_ref_head;
> > > +	atomic_t i_filelock_ref;
> > > 	u32 i_shared_gen;       /* increment each time we get FILE_SHARED */
> > > 	u32 i_rdcache_gen;      /* incremented each time we get FILE_CACHE. */
> > > 	u32 i_rdcache_revoking; /* RDCACHE gen to async invalidate, if any */
> > 
> > -- 
> > Jeff Layton <jlayton@redhat.com>
> 
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