Re: FAILED: patch "[PATCH] btrfs: do not zero f_bavail if we have available space" failed to apply to 5.5-stable tree

[Martin Steigerwald <martin@lichtvoll.de>]

Dear Greg,

gregkh@linuxfoundation.org - 09.02.20, 12:33:31 CET:
> The patch below does not apply to the 5.5-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git
> commit id to <stable@vger.kernel.org>.

I believe you tried to apply it twice, since it is already in 5.5.2.

Best,
Martin

> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
> From d55966c4279bfc6a0cf0b32bf13f5df228a1eeb6 Mon Sep 17 00:00:00 2001
> From: Josef Bacik <josef@toxicpanda.com>
> Date: Fri, 31 Jan 2020 09:31:05 -0500
> Subject: [PATCH] btrfs: do not zero f_bavail if we have available
> space
> 
> There was some logic added a while ago to clear out f_bavail in
> statfs() if we did not have enough free metadata space to satisfy our
> global reserve.  This was incorrect at the time, however didn't
> really pose a problem for normal file systems because we would often
> allocate chunks if we got this low on free metadata space, and thus
> wouldn't really hit this case unless we were actually full.
> 
> Fast forward to today and now we are much better about not allocating
> metadata chunks all of the time.  Couple this with d792b0f19711
> ("btrfs: always reserve our entire size for the global reserve")
> which now means we'll easily have a larger global reserve than our
> free space, we are now more likely to trip over this while still
> having plenty of space.
> 
> Fix this by skipping this logic if the global rsv's space_info is not
> full.  space_info->full is 0 unless we've attempted to allocate a
> chunk for that space_info and that has failed.  If this happens then
> the space for the global reserve is definitely sacred and we need to
> report b_avail == 0, but before then we can just use our calculated
> b_avail.
> 
> Reported-by: Martin Steigerwald <martin@lichtvoll.de>
> Fixes: ca8a51b3a979 ("btrfs: statfs: report zero available if metadata
> are exhausted") CC: stable@vger.kernel.org # 4.5+
> Reviewed-by: Qu Wenruo <wqu@suse.com>
> Tested-By: Martin Steigerwald <martin@lichtvoll.de>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Reviewed-by: David Sterba <dsterba@suse.com>
> Signed-off-by: David Sterba <dsterba@suse.com>
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index a906315efd19..0616a5434793 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2135,7 +2135,15 @@ static int btrfs_statfs(struct dentry *dentry,
> struct kstatfs *buf) */
>  	thresh = SZ_4M;
> 
> -	if (!mixed && total_free_meta - thresh < block_rsv->size)
> +	/*
> +	 * We only want to claim there's no available space if we can no
> longer +	 * allocate chunks for our metadata profile and our 
global
> reserve will +	 * not fit in the free metadata space.  If we aren't
> ->full then we +	 * still can allocate chunks and thus are fine using
> the currently +	 * calculated f_bavail.
> +	 */
> +	if (!mixed && block_rsv->space_info->full &&
> +	    total_free_meta - thresh < block_rsv->size)
>  		buf->f_bavail = 0;
> 
>  	buf->f_type = BTRFS_SUPER_MAGIC;


-- 
Martin