Description of problem:

Volume Name: arbvol
Type: Replicate
Volume ID: d7ccfadd-63e1-4fef-b70f-77d0e2cb2bba
Status: Started
Snapshot Count: 0
Number of Bricks: 1 x (2 + 1) = 3
Transport-type: tcp
Bricks:
Brick1: node1:/gluster/brick1/b1
Brick2: node2:/gluster/brick1/b1
Brick3: node3:/gluster/brick1/b1 (arbiter)
Options Reconfigured:
cluster.self-heal-daemon: off
performance.strict-o-direct: on
cluster.granular-entry-heal: enable
network.ping-timeout: 10
user.cifs: off
features.shard: on
cluster.shd-wait-qlength: 10000
cluster.shd-max-threads: 8
cluster.locking-scheme: granular
cluster.data-self-heal-algorithm: full
cluster.server-quorum-type: server
cluster.quorum-type: auto
cluster.eager-lock: on
network.remote-dio: off
performance.low-prio-threads: 32
performance.stat-prefetch: off
performance.io-cache: off
performance.read-ahead: off
performance.quick-read: off
transport.address-family: inet
nfs.disable: on
cluster.data-self-heal: off
cluster.metadata-self-heal: off
cluster.entry-self-heal: off

In a hc setup, writes, truncates and reads were happening from a single client while the bricks were continuously being killed and brought backup one by one in a loop. I/O was then getting hung from the mount.

gdb back trace  of mount:
#3  0x00007f45a762f5ee in shard_make_block_abspath (block_num=159197526, gfid=0x7f45a805a0a8 "$r\342\366{\260E\032\251\020\254>\312B\245\274", filepath=0x7f45ac9e1f90 "/.shard/2472e2f6-7bb0-451a-a910-ac3eca42a5bc.159197525", len=4096)
    at shard.c:57
#4  0x00007f45a7632605 in shard_common_resolve_shards (frame=0x7f45a8000b60, this=0x7f45a80121e0, post_res_handler=0x7f45a763a344 <shard_post_resolve_truncate_handler>) at shard.c:635
#5  0x00007f45a763337b in shard_refresh_dot_shard (frame=0x7f45a8000b60, this=0x7f45a80121e0) at shard.c:884
#6  0x00007f45a763b2a4 in shard_truncate_begin (frame=0x7f45a8000b60, this=0x7f45a80121e0) at shard.c:1989
#7  0x00007f45a763c7e3 in shard_post_lookup_truncate_handler (frame=0x7f45a8000b60, this=0x7f45a80121e0) at shard.c:2063
#8  0x00007f45a7634b79 in shard_lookup_base_file_cbk (frame=0x7f45a8000b60, cookie=0x7f45a804e130, this=0x7f45a80121e0, op_ret=0, op_errno=117, inode=0x7f45a805a0a0, buf=0x7f45a804ee68, xdata=0x7f45a8071ad0, postparent=0x7f45a804f098)
    at shard.c:1149
#9  0x00007f45a7892dd4 in dht_discover_complete (this=0x7f45a8010ab0, discover_frame=0x7f45a8060f60) at dht-common.c:577
#10 0x00007f45a78937f1 in dht_discover_cbk (frame=0x7f45a8060f60, cookie=0x7f45a800de50, this=0x7f45a8010ab0, op_ret=0, op_errno=117, inode=0x7f45a805a0a0, stbuf=0x7f45a807d890, xattr=0x7f45a8071ad0, postparent=0x7f45a807d900)
    at dht-common.c:700
#11 0x00007f45a7b71ad6 in afr_discover_done (frame=0x7f45a8066d60, this=0x7f45a800de50) at afr-common.c:2624
#12 0x00007f45a7b71e19 in afr_discover_cbk (frame=0x7f45a8066d60, cookie=0x2, this=0x7f45a800de50, op_ret=0, op_errno=0, inode=0x7f45a805a0a0, buf=0x7f45ac9e3900, xdata=0x7f45a806cb50, postparent=0x7f45ac9e3890) at afr-common.c:2669


shard_common_resolve_shards() was stuck in while (shard_idx_iter <= local->last_block) because local->last_block was -1. Turns out afr served the lookup from a bad copy (the good brick was down) and shard used the iatt values in the lookup cbk to calculate size and block count which were not correct.

xattr values of the FILE on the bad brick from which lookup was served:

[root@node2]# g /gluster/brick1/b1/FILE 
getfattr: Removing leading '/' from absolute path names
# file: gluster/brick1/b1/FILE
security.selinux=0x73797374656d5f753a6f626a6563745f723a676c7573746572645f627269636b5f743a733000
trusted.afr.arbvol-client-2=0x000003e00000046700000000
trusted.afr.dirty=0x000000020000012e00000000
trusted.gfid=0x0e47074be70b4c25bdf2f5d40a26a049
trusted.glusterfs.shard.block-size=0x0000000000400000
trusted.glusterfs.shard.file-size=0xfffffffffff214000000000000000000fffffffffffff80a0000000000000000