ceph: ceph_pagelist_append might sleep while atomic

Ceph's encode_caps_cb() worked hard to not call __page_cache_alloc()
while holding a lock, but it's spoiled because ceph_pagelist_addpage()
always calls kmap(), which might sleep.  Here's the result:

[13439.295457] ceph: mds0 reconnect start
[13439.300572] BUG: sleeping function called from invalid context at include/linux/highmem.h:58
[13439.309243] in_atomic(): 1, irqs_disabled(): 0, pid: 12059, name: kworker/1:1
    . . .
[13439.376225] Call Trace:
[13439.378757]  [<ffffffff81076f4c>] __might_sleep+0xfc/0x110
[13439.384353]  [<ffffffffa03f4ce0>] ceph_pagelist_append+0x120/0x1b0 [libceph]
[13439.391491]  [<ffffffffa0448fe9>] ceph_encode_locks+0x89/0x190 [ceph]
[13439.398035]  [<ffffffff814ee849>] ? _raw_spin_lock+0x49/0x50
[13439.403775]  [<ffffffff811cadf5>] ? lock_flocks+0x15/0x20
[13439.409277]  [<ffffffffa045e2af>] encode_caps_cb+0x41f/0x4a0 [ceph]
[13439.415622]  [<ffffffff81196748>] ? igrab+0x28/0x70
[13439.420610]  [<ffffffffa045e9f8>] ? iterate_session_caps+0xe8/0x250 [ceph]
[13439.427584]  [<ffffffffa045ea25>] iterate_session_caps+0x115/0x250 [ceph]
[13439.434499]  [<ffffffffa045de90>] ? set_request_path_attr+0x2d0/0x2d0 [ceph]
[13439.441646]  [<ffffffffa0462888>] send_mds_reconnect+0x238/0x450 [ceph]
[13439.448363]  [<ffffffffa0464542>] ? ceph_mdsmap_decode+0x5e2/0x770 [ceph]
[13439.455250]  [<ffffffffa0462e42>] check_new_map+0x352/0x500 [ceph]
[13439.461534]  [<ffffffffa04631ad>] ceph_mdsc_handle_map+0x1bd/0x260 [ceph]
[13439.468432]  [<ffffffff814ebc7e>] ? mutex_unlock+0xe/0x10
[13439.473934]  [<ffffffffa043c612>] extra_mon_dispatch+0x22/0x30 [ceph]
[13439.480464]  [<ffffffffa03f6c2c>] dispatch+0xbc/0x110 [libceph]
[13439.486492]  [<ffffffffa03eec3d>] process_message+0x1ad/0x1d0 [libceph]
[13439.493190]  [<ffffffffa03f1498>] ? read_partial_message+0x3e8/0x520 [libceph]
    . . .
[13439.587132] ceph: mds0 reconnect success
[13490.720032] ceph: mds0 caps stale
[13501.235257] ceph: mds0 recovery completed
[13501.300419] ceph: mds0 caps renewed

Fix it up by encoding locks into a buffer first, and when the number
of encoded locks is stable, copy that into a ceph_pagelist.

[elder@inktank.com: abbreviated the stack info a bit.]

Cc: stable@vger.kernel.org # 3.4+
Signed-off-by: Jim Schutt <jaschut@sandia.gov>
Reviewed-by: Alex Elder <elder@inktank.com>

fs/ceph/locks.c

@@ -191,70 +191,88 @@ void ceph_count_locks(struct inode *inode, int *fcntl_count, int *flock_count)
 }
 
 /**
- * Encode the flock and fcntl locks for the given inode into the pagelist.
- * Format is: #fcntl locks, sequential fcntl locks, #flock locks,
- * sequential flock locks.
- * Must be called with lock_flocks() already held.
- * If we encounter more of a specific lock type than expected,
- * we return the value 1.
+ * Encode the flock and fcntl locks for the given inode into the ceph_filelock
+ * array. Must be called with lock_flocks() already held.
+ * If we encounter more of a specific lock type than expected, return -ENOSPC.
  */
-int ceph_encode_locks(struct inode *inode, struct ceph_pagelist *pagelist,
-		      int num_fcntl_locks, int num_flock_locks)
+int ceph_encode_locks_to_buffer(struct inode *inode,
+				struct ceph_filelock *flocks,
+				int num_fcntl_locks, int num_flock_locks)
 {
 	struct file_lock *lock;
-	struct ceph_filelock cephlock;
 	int err = 0;
 	int seen_fcntl = 0;
 	int seen_flock = 0;
-	__le32 nlocks;
+	int l = 0;
 
 	dout("encoding %d flock and %d fcntl locks", num_flock_locks,
 	     num_fcntl_locks);
-	nlocks = cpu_to_le32(num_fcntl_locks);
-	err = ceph_pagelist_append(pagelist, &nlocks, sizeof(nlocks));
-	if (err)
-		goto fail;
+
 	for (lock = inode->i_flock; lock != NULL; lock = lock->fl_next) {
 		if (lock->fl_flags & FL_POSIX) {
 			++seen_fcntl;
 			if (seen_fcntl > num_fcntl_locks) {
 				err = -ENOSPC;
 				goto fail;
 			}
-			err = lock_to_ceph_filelock(lock, &cephlock);
+			err = lock_to_ceph_filelock(lock, &flocks[l]);
 			if (err)
 				goto fail;
-			err = ceph_pagelist_append(pagelist, &cephlock,
-					   sizeof(struct ceph_filelock));
+			++l;
 		}
-		if (err)
-			goto fail;
 	}
-
-	nlocks = cpu_to_le32(num_flock_locks);
-	err = ceph_pagelist_append(pagelist, &nlocks, sizeof(nlocks));
-	if (err)
-		goto fail;
 	for (lock = inode->i_flock; lock != NULL; lock = lock->fl_next) {
 		if (lock->fl_flags & FL_FLOCK) {
 			++seen_flock;
 			if (seen_flock > num_flock_locks) {
 				err = -ENOSPC;
 				goto fail;
 			}
-			err = lock_to_ceph_filelock(lock, &cephlock);
+			err = lock_to_ceph_filelock(lock, &flocks[l]);
 			if (err)
 				goto fail;
-			err = ceph_pagelist_append(pagelist, &cephlock,
-					   sizeof(struct ceph_filelock));
+			++l;
 		}
-		if (err)
-			goto fail;
 	}
 fail:
 	return err;
 }
 
+/**
+ * Copy the encoded flock and fcntl locks into the pagelist.
+ * Format is: #fcntl locks, sequential fcntl locks, #flock locks,
+ * sequential flock locks.
+ * Returns zero on success.
+ */
+int ceph_locks_to_pagelist(struct ceph_filelock *flocks,
+			   struct ceph_pagelist *pagelist,
+			   int num_fcntl_locks, int num_flock_locks)
+{
+	int err = 0;
+	__le32 nlocks;
+
+	nlocks = cpu_to_le32(num_fcntl_locks);
+	err = ceph_pagelist_append(pagelist, &nlocks, sizeof(nlocks));
+	if (err)
+		goto out_fail;
+
+	err = ceph_pagelist_append(pagelist, flocks,
+				   num_fcntl_locks * sizeof(*flocks));
+	if (err)
+		goto out_fail;
+
+	nlocks = cpu_to_le32(num_flock_locks);
+	err = ceph_pagelist_append(pagelist, &nlocks, sizeof(nlocks));
+	if (err)
+		goto out_fail;
+
+	err = ceph_pagelist_append(pagelist,
+				   &flocks[num_fcntl_locks],
+				   num_flock_locks * sizeof(*flocks));
+out_fail:
+	return err;
+}
+
 /*
  * Given a pointer to a lock, convert it to a ceph filelock
  */

fs/ceph/mds_client.c

@@ -2478,39 +2478,44 @@ static int encode_caps_cb(struct inode *inode, struct ceph_cap *cap,
 
 	if (recon_state->flock) {
 		int num_fcntl_locks, num_flock_locks;
-		struct ceph_pagelist_cursor trunc_point;
-
-		ceph_pagelist_set_cursor(pagelist, &trunc_point);
-		do {
-			lock_flocks();
-			ceph_count_locks(inode, &num_fcntl_locks,
-					 &num_flock_locks);
-			rec.v2.flock_len = cpu_to_le32(2*sizeof(u32) +
-					    (num_fcntl_locks+num_flock_locks) *
-					    sizeof(struct ceph_filelock));
-			unlock_flocks();
-
-			/* pre-alloc pagelist */
-			ceph_pagelist_truncate(pagelist, &trunc_point);
-			err = ceph_pagelist_append(pagelist, &rec, reclen);
-			if (!err)
-				err = ceph_pagelist_reserve(pagelist,
-							    rec.v2.flock_len);
-
-			/* encode locks */
-			if (!err) {
-				lock_flocks();
-				err = ceph_encode_locks(inode,
-							pagelist,
-							num_fcntl_locks,
-							num_flock_locks);
-				unlock_flocks();
-			}
-		} while (err == -ENOSPC);
+		struct ceph_filelock *flocks;
+
+encode_again:
+		lock_flocks();
+		ceph_count_locks(inode, &num_fcntl_locks, &num_flock_locks);
+		unlock_flocks();
+		flocks = kmalloc((num_fcntl_locks+num_flock_locks) *
+				 sizeof(struct ceph_filelock), GFP_NOFS);
+		if (!flocks) {
+			err = -ENOMEM;
+			goto out_free;
+		}
+		lock_flocks();
+		err = ceph_encode_locks_to_buffer(inode, flocks,
+						  num_fcntl_locks,
+						  num_flock_locks);
+		unlock_flocks();
+		if (err) {
+			kfree(flocks);
+			if (err == -ENOSPC)
+				goto encode_again;
+			goto out_free;
+		}
+		/*
+		 * number of encoded locks is stable, so copy to pagelist
+		 */
+		rec.v2.flock_len = cpu_to_le32(2*sizeof(u32) +
+				    (num_fcntl_locks+num_flock_locks) *
+				    sizeof(struct ceph_filelock));
+		err = ceph_pagelist_append(pagelist, &rec, reclen);
+		if (!err)
+			err = ceph_locks_to_pagelist(flocks, pagelist,
+						     num_fcntl_locks,
+						     num_flock_locks);
+		kfree(flocks);
 	} else {
 		err = ceph_pagelist_append(pagelist, &rec, reclen);
 	}
-
 out_free:
 	kfree(path);
 out_dput:

fs/ceph/super.h

@@ -822,8 +822,13 @@ extern const struct export_operations ceph_export_ops;
 extern int ceph_lock(struct file *file, int cmd, struct file_lock *fl);
 extern int ceph_flock(struct file *file, int cmd, struct file_lock *fl);
 extern void ceph_count_locks(struct inode *inode, int *p_num, int *f_num);
-extern int ceph_encode_locks(struct inode *i, struct ceph_pagelist *p,
-			     int p_locks, int f_locks);
+extern int ceph_encode_locks_to_buffer(struct inode *inode,
+				       struct ceph_filelock *flocks,
+				       int num_fcntl_locks,
+				       int num_flock_locks);
+extern int ceph_locks_to_pagelist(struct ceph_filelock *flocks,
+				  struct ceph_pagelist *pagelist,
+				  int num_fcntl_locks, int num_flock_locks);
 extern int lock_to_ceph_filelock(struct file_lock *fl, struct ceph_filelock *c);
 
 /* debugfs.c */