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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eli V <eliventer@gmail.com>,
        Anand Jain <anand.jain@oracle.com>, Qu Wenruo <wqu@suse.com>,
        David Sterba <dsterba@suse.com>
Subject: [PATCH 5.10 025/103] btrfs: prevent __btrfs_dump_space_info() to underflow its free space
Date:   Mon, 27 Sep 2021 19:01:57 +0200
Message-Id: <20210927170226.596035148@linuxfoundation.org>
In-Reply-To: <20210927170225.702078779@linuxfoundation.org>
References: <20210927170225.702078779@linuxfoundation.org>
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From: Qu Wenruo <wqu@suse.com>

commit 0619b7901473c380abc05d45cf9c70bee0707db3 upstream.

It's not uncommon where __btrfs_dump_space_info() gets called
under over-commit situations.

In that case free space would underflow as total allocated space is not
enough to handle all the over-committed space.

Such underflow values can sometimes cause confusion for users enabled
enospc_debug mount option, and takes some seconds for developers to
convert the underflow value to signed result.

Just output the free space as s64 to avoid such problem.

Reported-by: Eli V <eliventer@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAJtFHUSy4zgyhf-4d9T+KdJp9w=UgzC2A0V=VtmaeEpcGgm1-Q@mail.gmail.com/
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/btrfs/space-info.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -417,9 +417,10 @@ static void __btrfs_dump_space_info(stru
 {
 	lockdep_assert_held(&info->lock);
 
-	btrfs_info(fs_info, "space_info %llu has %llu free, is %sfull",
+	/* The free space could be negative in case of overcommit */
+	btrfs_info(fs_info, "space_info %llu has %lld free, is %sfull",
 		   info->flags,
-		   info->total_bytes - btrfs_space_info_used(info, true),
+		   (s64)(info->total_bytes - btrfs_space_info_used(info, true)),
 		   info->full ? "" : "not ");
 	btrfs_info(fs_info,
 		"space_info total=%llu, used=%llu, pinned=%llu, reserved=%llu, may_use=%llu, readonly=%llu",