This is a note to let you know that I've just added the patch titled
btrfs: fix race between extent freeing/allocation when using bitmaps
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-race-between-extent-freeing-allocation-when-using-bitmaps.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 3c17916510428dbccdf657de050c34e208347089 Mon Sep 17 00:00:00 2001
From: Nikolay Borisov <nborisov@xxxxxxxx>
Date: Mon, 8 Feb 2021 10:26:54 +0200
Subject: btrfs: fix race between extent freeing/allocation when using bitmaps
From: Nikolay Borisov <nborisov@xxxxxxxx>
commit 3c17916510428dbccdf657de050c34e208347089 upstream.
During allocation the allocator will try to allocate an extent using
cluster policy. Once the current cluster is exhausted it will remove the
entry under btrfs_free_cluster::lock and subsequently acquire
btrfs_free_space_ctl::tree_lock to dispose of the already-deleted entry
and adjust btrfs_free_space_ctl::total_bitmap. This poses a problem
because there exists a race condition between removing the entry under
one lock and doing the necessary accounting holding a different lock
since extent freeing only uses the 2nd lock. This can result in the
following situation:
T1: T2:
btrfs_alloc_from_cluster insert_into_bitmap <holds tree_lock>
if (entry->bytes == 0) if (block_group && !list_empty(&block_group->cluster_list)) {
rb_erase(entry)
spin_unlock(&cluster->lock);
(total_bitmaps is still 4) spin_lock(&cluster->lock);
<doesn't find entry in cluster->root>
spin_lock(&ctl->tree_lock); <goes to new_bitmap label, adds
<blocked since T2 holds tree_lock> <a new entry and calls add_new_bitmap>
recalculate_thresholds <crashes,
due to total_bitmaps
becoming 5 and triggering
an ASSERT>
To fix this ensure that once depleted, the cluster entry is deleted when
both cluster lock and tree locks are held in the allocator (T1), this
ensures that even if there is a race with a concurrent
insert_into_bitmap call it will correctly find the entry in the cluster
and add the new space to it.
CC: <stable@xxxxxxxxxxxxxxx> # 4.4+
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/free-space-cache.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -3034,8 +3034,6 @@ u64 btrfs_alloc_from_cluster(struct btrf
entry->bytes -= bytes;
}
- if (entry->bytes == 0)
- rb_erase(&entry->offset_index, &cluster->root);
break;
}
out:
@@ -3052,7 +3050,10 @@ out:
ctl->free_space -= bytes;
if (!entry->bitmap && !btrfs_free_space_trimmed(entry))
ctl->discardable_bytes[BTRFS_STAT_CURR] -= bytes;
+
+ spin_lock(&cluster->lock);
if (entry->bytes == 0) {
+ rb_erase(&entry->offset_index, &cluster->root);
ctl->free_extents--;
if (entry->bitmap) {
kmem_cache_free(btrfs_free_space_bitmap_cachep,
@@ -3065,6 +3066,7 @@ out:
kmem_cache_free(btrfs_free_space_cachep, entry);
}
+ spin_unlock(&cluster->lock);
spin_unlock(&ctl->tree_lock);
return ret;
Patches currently in stable-queue which might be from nborisov@xxxxxxxx are
queue-5.10/btrfs-fix-race-between-extent-freeing-allocation-when-using-bitmaps.patch
queue-5.10/btrfs-free-correct-amount-of-space-in-btrfs_delayed_inode_reserve_metadata.patch
queue-5.10/btrfs-unlock-extents-in-btrfs_zero_range-in-case-of-quota-reservation-errors.patch
