linux-kernel - [PATCH] btrfs: Remove unused variable in btrfs_{start,write}_dirty_block

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Message-Id: <20220324153644.4079376-1-nathan@kernel.org>
Date:   Thu, 24 Mar 2022 08:36:45 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev,
        Nathan Chancellor <nathan@...nel.org>, stable@...r.kernel.org
Subject: [PATCH] btrfs: Remove unused variable in btrfs_{start,write}_dirty_block_groups()

Clang's version of -Wunused-but-set-variable recently gained support for
unary operations, which reveals two unused variables:

  fs/btrfs/block-group.c:2949:6: error: variable 'num_started' set but not used [-Werror,-Wunused-but-set-variable]
          int num_started = 0;
              ^
  fs/btrfs/block-group.c:3116:6: error: variable 'num_started' set but not used [-Werror,-Wunused-but-set-variable]
          int num_started = 0;
              ^
  2 errors generated.

These variables appear to be unused from their introduction, so just
remove them to silence the warnings.

Cc: stable@...r.kernel.org
Fixes: c9dc4c657850 ("Btrfs: two stage dirty block group writeout")
Fixes: 1bbc621ef284 ("Btrfs: allow block group cache writeout outside critical section in commit")
Link: https://github.com/ClangBuiltLinux/linux/issues/1614
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---

I am requesting a stable backport because this is visible with
allmodconfig, which enables CONFIG_WERROR, breaking the build.

To quote Linus:

"EVERYBODY should have CONFIG_WERROR=y on at least x86-64 and other
serious architectures, unless you have some completely random
experimental (and broken) compiler."

https://lore.kernel.org/r/CAHk-=wifoM9VOp-55OZCRcO9MnqQ109UTuCiXeZ-eyX_JcNVGg@mail.gmail.com/

 fs/btrfs/block-group.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index c22d287e020b..9ad265066225 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2946,7 +2946,6 @@ int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans)
 	struct btrfs_path *path = NULL;
 	LIST_HEAD(dirty);
 	struct list_head *io = &cur_trans->io_bgs;
-	int num_started = 0;
 	int loops = 0;
 
 	spin_lock(&cur_trans->dirty_bgs_lock);
@@ -3012,7 +3011,6 @@ int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans)
 			cache->io_ctl.inode = NULL;
 			ret = btrfs_write_out_cache(trans, cache, path);
 			if (ret == 0 && cache->io_ctl.inode) {
-				num_started++;
 				should_put = 0;
 
 				/*
@@ -3113,7 +3111,6 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans)
 	int should_put;
 	struct btrfs_path *path;
 	struct list_head *io = &cur_trans->io_bgs;
-	int num_started = 0;
 
 	path = btrfs_alloc_path();
 	if (!path)
@@ -3171,7 +3168,6 @@ int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans)
 			cache->io_ctl.inode = NULL;
 			ret = btrfs_write_out_cache(trans, cache, path);
 			if (ret == 0 && cache->io_ctl.inode) {
-				num_started++;
 				should_put = 0;
 				list_add_tail(&cache->io_list, io);
 			} else {

base-commit: d3e29967079c522ce1c5cab0e9fab2c280b977eb
-- 
2.35.1