[LU-15513] crash in lod_fill_mirrors() with sparse OSTs + PFL

• Type: Bug
• Resolution: Fixed
• Priority: Critical
• Fix Version/s: Lustre 2.16.0
• Affects Version/s: Lustre 2.15.0
• Severity: 3
• Assignee: Zhenyu Xu
• Reporter: Andreas Dilger

Description

MDS can crash in lod_fill_mirrors() if a default PFL layout is set on a directory, and the filesystem has sparse OST indices:

BUG: unable to handle kernel NULL pointer dereference at 00000000000000e8
IP: [<ffffffffc17a0e6e>] lod_fill_mirrors+0x17e/0x490 [lod]
Oops: 0000 [#1] SMP 
CPU: 8 PID: 16061 Comm: mdt02_001 Kdump: loaded 3.10.0-1160.49.1.el7_lustre.x86_64 #1
Call Trace:
 lod_striped_create+0x3d7/0x690 [lod]
 lod_layout_change+0x3f/0x50 [lod]
 mdd_layout_change+0xaea/0xef0 [mdd]
 mdt_layout_change+0x2df/0x480 [mdt]
 mdt_intent_layout+0x8a0/0xe00 [mdt]
 mdt_intent_policy+0x435/0xd80 [mdt]
 ldlm_lock_enqueue+0x376/0x9b0 [ptlrpc]
 ldlm_handle_enqueue0+0xaa6/0x1630 [ptlrpc]
 tgt_enqueue+0x62/0x210 [ptlrpc]
 tgt_request_handle+0xaee/0x15f0 [ptlrpc]
 ptlrpc_server_handle_request+0x24b/0xab0 [ptlrpc]
 ptlrpc_main+0xb34/0x1470 [ptlrpc]

This results in the lod_tgt_osts[] array being sparse and have NULL pointers that are accessed when checking for non-rotational OSTs.

(gdb) list *(lod_fill_mirrors+0x17e)
0xfe9e is in lod_fill_mirrors (/usr/src/lustre-exa-52/lustre/lod/lod_lov.c:768).
757             for (i = 0; i < lo->ldo_comp_cnt; i++, lod_comp++) {
758                     int stale = !!(lod_comp->llc_flags & LCME_FL_STALE);
759                     int preferred = !!(lod_comp->llc_flags & LCME_FL_PREF_WR);
760                     int j;
761
762                     pref = 0;
763                     /* calculate component preference over all used OSTs */
764                     for (j = 0; j < lod_comp->llc_stripes_allocated; j++) {
765                             int idx = lod_comp->llc_ost_indices[j];
766                             struct obd_statfs *osfs = &OST_TGT(lod,idx)->ltd_statfs;
767
768                             if (osfs->os_state & OS_STATE_NONROT)
769                                     pref++;
770                     }
771
772                     if (mirror_id_of(lod_comp->llc_id) == mirror_id) {
(gdb) p &((struct lod_tgt_desc *)0)->ltd_statfs + &((struct obd_statfs *)0)->os_state
$1 = 0xe8

Issue Links

• is related to: LU-14996 select preferred mirror using non-rotational status