From 4f0aa008ed393d7ce222c4ea4bd0fa6ed52b48f6 Mon Sep 17 00:00:00 2001

From: Krutika Dhananjay <kdhananj@redhat.com>

Date: Fri, 5 Apr 2019 12:29:23 +0530

Subject: [PATCH 177/178] features/shard: Fix extra unref when inode object is

 lru'd out and added back

Long tale of double unref! But do read...

In cases where a shard base inode is evicted from lru list while still

being part of fsync list but added back soon before its unlink, there

could be an extra inode_unref() leading to premature inode destruction

leading to crash.

One such specific case is the following -

Consider features.shard-deletion-rate = features.shard-lru-limit = 2.

This is an oversimplified example but explains the problem clearly.

First, a file is FALLOCATE'd to a size so that number of shards under

/.shard = 3 > lru-limit.

Shards 1, 2 and 3 need to be resolved. 1 and 2 are resolved first.

Resultant lru list:

                               1 -----> 2

refs on base inode -          (1)  +   (1) = 2

3 needs to be resolved. So 1 is lru'd out. Resultant lru list -

		               2 -----> 3

refs on base inode -          (1)  +   (1) = 2

Note that 1 is inode_unlink()d but not destroyed because there are

non-zero refs on it since it is still participating in this ongoing

FALLOCATE operation.

FALLOCATE is sent on all participant shards. In the cbk, all of them are

added to fync_list.

Resulting fsync list -

                               1 -----> 2 -----> 3 (order doesn't matter)

refs on base inode -          (1)  +   (1)  +   (1) = 3

Total refs = 3 + 2 = 5

Now an attempt is made to unlink this file. Background deletion is triggered.

The first $shard-deletion-rate shards need to be unlinked in the first batch.

So shards 1 and 2 need to be resolved. inode_resolve fails on 1 but succeeds

on 2 and so it's moved to tail of list.

lru list now -

                              3 -----> 2

No change in refs.

shard 1 is looked up. In lookup_cbk, it's linked and added back to lru list

at the cost of evicting shard 3.

lru list now -

                              2 -----> 1

refs on base inode:          (1)  +   (1) = 2

fsync list now -

                              1 -----> 2 (again order doesn't matter)

refs on base inode -         (1)  +   (1) = 2

Total refs = 2 + 2 = 4

After eviction, it is found 3 needs fsync. So fsync is wound, yet to be ack'd.

So it is still inode_link()d.

Now deletion of shards 1 and 2 completes. lru list is empty. Base inode unref'd and

destroyed.

In the next batched deletion, 3 needs to be deleted. It is inode_resolve()able.

It is added back to lru list but base inode passed to __shard_update_shards_inode_list()

is NULL since the inode is destroyed. But its ctx->inode still contains base inode ptr

from first addition to lru list for no additional ref on it.

lru list now -

                              3

refs on base inode -         (0)

Total refs on base inode = 0

Unlink is sent on 3. It completes. Now since the ctx contains ptr to base_inode and the

shard is part of lru list, base shard is unref'd leading to a crash.

FIX:

When shard is readded back to lru list, copy the base inode pointer as is into its inode ctx,

even if it is NULL. This is needed to prevent double unrefs at the time of deleting it.

Upstream patch:

> BUG: 1696136

> Upstream patch link: https://review.gluster.org/c/glusterfs/+/22517

> Change-Id: I99a44039da2e10a1aad183e84f644d63ca552462

> Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>

Change-Id: I99a44039da2e10a1aad183e84f644d63ca552462

Updates: bz#1694595

Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>

Reviewed-on: https://code.engineering.redhat.com/gerrit/172803

Tested-by: RHGS Build Bot <nigelb@redhat.com>

Reviewed-by: Atin Mukherjee <amukherj@redhat.com>

---

 .../bug-1696136-lru-limit-equals-deletion-rate.t   | 34 ++++++++++++++++++++++

 xlators/features/shard/src/shard.c                 |  6 ++--

 2 files changed, 36 insertions(+), 4 deletions(-)

 create mode 100644 tests/bugs/shard/bug-1696136-lru-limit-equals-deletion-rate.t

diff --git a/tests/bugs/shard/bug-1696136-lru-limit-equals-deletion-rate.t b/tests/bugs/shard/bug-1696136-lru-limit-equals-deletion-rate.t

new file mode 100644

index 0000000..3e4a65a

--- /dev/null

+++ b/tests/bugs/shard/bug-1696136-lru-limit-equals-deletion-rate.t

@@ -0,0 +1,34 @@

+#!/bin/bash

+

+. $(dirname $0)/../../include.rc

+. $(dirname $0)/../../volume.rc

+. $(dirname $0)/../../fallocate.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 120

+TEST $CLI volume set $V0 features.shard-deletion-rate 120

+TEST $CLI volume set $V0 performance.write-behind off

+TEST $CLI volume start $V0

+

+TEST $GFS --volfile-id=$V0 --volfile-server=$H0 $M0

+

+TEST build_tester $(dirname $0)/bug-1696136.c -lgfapi -Wall -O2

+

+# Create a file

+TEST touch $M0/file1

+

+# Fallocate a 500M file. This will make sure number of participant shards are > lru-limit

+TEST $(dirname $0)/bug-1696136 $H0 $V0 "0" "0" "536870912" /file1 `gluster --print-logdir`/glfs-$V0.log

+

+EXPECT_WITHIN $UMOUNT_TIMEOUT "Y" force_umount $M0

+TEST $CLI volume stop $V0

+TEST $CLI volume delete $V0

+rm -f $(dirname $0)/bug-1696136

+

+cleanup

diff --git a/xlators/features/shard/src/shard.c b/xlators/features/shard/src/shard.c

index 3c4bcdc..c1799ad 100644

--- a/xlators/features/shard/src/shard.c

+++ b/xlators/features/shard/src/shard.c

@@ -689,8 +689,7 @@ __shard_update_shards_inode_list(inode_t *linked_inode, xlator_t *this,

             ctx->block_num = block_num;

             list_add_tail(&ctx->ilist, &priv->ilist_head);

             priv->inode_count++;

-            if (base_inode)

-                ctx->base_inode = inode_ref(base_inode);

+            ctx->base_inode = inode_ref(base_inode);

         } else {

             /*If on the other hand there is no available slot for this inode

              * in the list, delete the lru inode from the head of the list,

@@ -765,8 +764,7 @@ __shard_update_shards_inode_list(inode_t *linked_inode, xlator_t *this,

             else

                 gf_uuid_copy(ctx->base_gfid, gfid);

             ctx->block_num = block_num;

-            if (base_inode)

-                ctx->base_inode = inode_ref(base_inode);

+            ctx->base_inode = inode_ref(base_inode);

             list_add_tail(&ctx->ilist, &priv->ilist_head);

         }

     } else {

-- 

1.8.3.1