features/shard: Hold a ref on base inode when adding a shard to lru list

In __shard_update_shards_inode_list(), previously shard translator
was not holding a ref on the base inode whenever a shard was added to
the lru list. But if the base shard is forgotten and destroyed either
by fuse due to memory pressure or due to the file being deleted at some
point by a different client with this client still containing stale
shards in its lru list, the client would crash at the time of locking
lru_base_inode->lock owing to illegal memory access.

So now the base shard is ref'd into the inode ctx of every shard that
is added to lru list until it gets lru'd out.

The patch also handles the case where none of the shards associated
with a file that is about to be deleted are part of the LRU list and
where an unlink at the beginning of the operation destroys the base
inode (because there are no refkeepers) and hence all of the shards
that are about to be deleted will be resolved without the existence
of a base shard in-memory. This, if not handled properly, could lead
to a crash.

Change-Id: Ic15ca41444dd04684a9458bd4a526b1d3e160499
updates: bz#1605056
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/tests/bugs/shard/bug-1605056-2.t b/tests/bugs/shard/bug-1605056-2.t
new file mode 100644
index 00000000000..a9c10fec3ea
--- /dev/null
+++ b/tests/bugs/shard/bug-1605056-2.t
@@ -0,0 +1,34 @@
+#!/bin/bash
+
+. $(dirname $0)/../../include.rc
+. $(dirname $0)/../../volume.rc
+
+cleanup
+
+TEST glusterd
+TEST pidof glusterd
+TEST $CLI volume create $V0 replica 3 $H0:$B0/${V0}{0,1,2}
+TEST $CLI volume set $V0 features.shard on
+TEST $CLI volume set $V0 features.shard-block-size 4MB
+TEST $CLI volume set $V0 features.shard-lru-limit 25
+TEST $CLI volume set $V0 performance.write-behind off
+
+TEST $CLI volume start $V0
+
+TEST $GFS --volfile-id=$V0 --volfile-server=$H0 $M0
+
+# Perform a write that would cause 25 shards to be created under .shard
+TEST dd if=/dev/zero of=$M0/foo bs=1M count=104
+
+# Write into another file bar to ensure all of foo's shards are evicted from lru list of $M0
+TEST dd if=/dev/zero of=$M0/bar bs=1M count=104
+
+# Delete foo from $M0. If there's a bug, the mount will crash.
+TEST unlink $M0/foo
+
+EXPECT_WITHIN $UMOUNT_TIMEOUT "Y" force_umount $M0
+
+TEST $CLI volume stop $V0
+TEST $CLI volume delete $V0
+
+cleanup