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>

1 files changed, 35 insertions, 30 deletions

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index d9ca1525547..4d2920304be 100644
--- a/fs/ceph/mds_client.c
+++ b/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: