Re: [PATCH v2 2/2] Move BTRFS RCU string to common library

[josh@joshtriplett.org]

On Fri, Sep 19, 2014 at 02:01:30AM -0700, Omar Sandoval wrote:
> The RCU-friendy string API used internally by BTRFS is generic enough for
> common use. This doesn't add any new functionality, but instead just moves the
> code and documents the existing API.
> 
> Signed-off-by: Omar Sandoval <osandov@osandov.com>

One nit: shouldn't the returned rcu_string pointer have an __rcu
address space annotation?

With that fixed:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  fs/btrfs/check-integrity.c |  6 +--
>  fs/btrfs/dev-replace.c     | 19 +++++-----
>  fs/btrfs/disk-io.c         |  6 +--
>  fs/btrfs/extent_io.c       |  4 +-
>  fs/btrfs/ioctl.c           |  4 +-
>  fs/btrfs/raid56.c          |  2 +-
>  fs/btrfs/rcu-string.h      | 56 ----------------------------
>  fs/btrfs/scrub.c           | 15 ++++----
>  fs/btrfs/super.c           |  2 +-
>  fs/btrfs/volumes.c         | 14 +++----
>  include/linux/rcustring.h  | 91 ++++++++++++++++++++++++++++++++++++++++++++++
>  11 files changed, 128 insertions(+), 91 deletions(-)
>  delete mode 100644 fs/btrfs/rcu-string.h
>  create mode 100644 include/linux/rcustring.h
> 
> diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
> index ce92ae3..4ccd7da 100644
> --- a/fs/btrfs/check-integrity.c
> +++ b/fs/btrfs/check-integrity.c
> @@ -94,6 +94,7 @@
>  #include <linux/mutex.h>
>  #include <linux/genhd.h>
>  #include <linux/blkdev.h>
> +#include <linux/rcustring.h>
>  #include "ctree.h"
>  #include "disk-io.h"
>  #include "hash.h"
> @@ -103,7 +104,6 @@
>  #include "print-tree.h"
>  #include "locking.h"
>  #include "check-integrity.h"
> -#include "rcu-string.h"
>  
>  #define BTRFSIC_BLOCK_HASHTABLE_SIZE 0x10000
>  #define BTRFSIC_BLOCK_LINK_HASHTABLE_SIZE 0x10000
> @@ -851,8 +851,8 @@ static int btrfsic_process_superblock_dev_mirror(
>  			printk_in_rcu(KERN_INFO "New initial S-block (bdev %p, %s)"
>  				     " @%llu (%s/%llu/%d)\n",
>  				     superblock_bdev,
> -				     rcu_str_deref(device->name), dev_bytenr,
> -				     dev_state->name, dev_bytenr,
> +				     rcu_string_dereference(device->name),
> +				     dev_bytenr, dev_state->name, dev_bytenr,
>  				     superblock_mirror_num);
>  		list_add(&superblock_tmp->all_blocks_node,
>  			 &state->all_blocks_list);
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index eea26e1..87d10cc 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -25,6 +25,7 @@
>  #include <linux/capability.h>
>  #include <linux/kthread.h>
>  #include <linux/math64.h>
> +#include <linux/rcustring.h>
>  #include <asm/div64.h>
>  #include "ctree.h"
>  #include "extent_map.h"
> @@ -34,7 +35,6 @@
>  #include "volumes.h"
>  #include "async-thread.h"
>  #include "check-integrity.h"
> -#include "rcu-string.h"
>  #include "dev-replace.h"
>  #include "sysfs.h"
>  
> @@ -376,9 +376,9 @@ int btrfs_dev_replace_start(struct btrfs_root *root,
>  	printk_in_rcu(KERN_INFO
>  		      "BTRFS: dev_replace from %s (devid %llu) to %s started\n",
>  		      src_device->missing ? "<missing disk>" :
> -		        rcu_str_deref(src_device->name),
> +		      rcu_string_dereference(src_device->name),
>  		      src_device->devid,
> -		      rcu_str_deref(tgt_device->name));
> +		      rcu_string_dereference(tgt_device->name));
>  
>  	tgt_device->total_bytes = src_device->total_bytes;
>  	tgt_device->disk_total_bytes = src_device->disk_total_bytes;
> @@ -528,9 +528,10 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
>  		printk_in_rcu(KERN_ERR
>  			      "BTRFS: btrfs_scrub_dev(%s, %llu, %s) failed %d\n",
>  			      src_device->missing ? "<missing disk>" :
> -			        rcu_str_deref(src_device->name),
> +			      rcu_string_dereference(src_device->name),
>  			      src_device->devid,
> -			      rcu_str_deref(tgt_device->name), scrub_ret);
> +			      rcu_string_dereference(tgt_device->name),
> +			      scrub_ret);
>  		btrfs_dev_replace_unlock(dev_replace);
>  		mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
>  		mutex_unlock(&root->fs_info->chunk_mutex);
> @@ -544,9 +545,9 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
>  	printk_in_rcu(KERN_INFO
>  		      "BTRFS: dev_replace from %s (devid %llu) to %s) finished\n",
>  		      src_device->missing ? "<missing disk>" :
> -		        rcu_str_deref(src_device->name),
> +		      rcu_string_dereference(src_device->name),
>  		      src_device->devid,
> -		      rcu_str_deref(tgt_device->name));
> +		      rcu_string_dereference(tgt_device->name));
>  	tgt_device->is_tgtdev_for_dev_replace = 0;
>  	tgt_device->devid = src_device->devid;
>  	src_device->devid = BTRFS_DEV_REPLACE_DEVID;
> @@ -805,10 +806,10 @@ static int btrfs_dev_replace_kthread(void *data)
>  		printk_in_rcu(KERN_INFO
>  			"BTRFS: continuing dev_replace from %s (devid %llu) to %s @%u%%\n",
>  			dev_replace->srcdev->missing ? "<missing disk>" :
> -			rcu_str_deref(dev_replace->srcdev->name),
> +			rcu_string_dereference(dev_replace->srcdev->name),
>  			dev_replace->srcdev->devid,
>  			dev_replace->tgtdev ?
> -			rcu_str_deref(dev_replace->tgtdev->name) :
> +			rcu_string_dereference(dev_replace->tgtdev->name) :
>  			"<missing target disk>",
>  			(unsigned int)progress);
>  	}
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index a1d36e6..00f7441 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -31,6 +31,7 @@
>  #include <linux/ratelimit.h>
>  #include <linux/uuid.h>
>  #include <linux/semaphore.h>
> +#include <linux/rcustring.h>
>  #include <asm/unaligned.h>
>  #include "ctree.h"
>  #include "disk-io.h"
> @@ -44,7 +45,6 @@
>  #include "free-space-cache.h"
>  #include "inode-map.h"
>  #include "check-integrity.h"
> -#include "rcu-string.h"
>  #include "dev-replace.h"
>  #include "raid56.h"
>  #include "sysfs.h"
> @@ -3059,7 +3059,7 @@ static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
>  
>  		printk_ratelimited_in_rcu(KERN_WARNING "BTRFS: lost page write due to "
>  					  "I/O error on %s\n",
> -					  rcu_str_deref(device->name));
> +					  rcu_string_dereference(device->name));
>  		/* note, we dont' set_buffer_write_io_error because we have
>  		 * our own ways of dealing with the IO errors
>  		 */
> @@ -3247,7 +3247,7 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
>  
>  		if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
>  			printk_in_rcu("BTRFS: disabling barriers on dev %s\n",
> -				      rcu_str_deref(device->name));
> +				      rcu_string_dereference(device->name));
>  			device->nobarriers = 1;
>  		} else if (!bio_flagged(bio, BIO_UPTODATE)) {
>  			ret = -EIO;
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index af0359d..441dccd 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -11,6 +11,7 @@
>  #include <linux/pagevec.h>
>  #include <linux/prefetch.h>
>  #include <linux/cleancache.h>
> +#include <linux/rcustring.h>
>  #include "extent_io.h"
>  #include "extent_map.h"
>  #include "ctree.h"
> @@ -18,7 +19,6 @@
>  #include "volumes.h"
>  #include "check-integrity.h"
>  #include "locking.h"
> -#include "rcu-string.h"
>  #include "backref.h"
>  
>  static struct kmem_cache *extent_state_cache;
> @@ -2065,7 +2065,7 @@ int repair_io_failure(struct btrfs_fs_info *fs_info, u64 start,
>  	printk_ratelimited_in_rcu(KERN_INFO
>  			"BTRFS: read error corrected: ino %lu off %llu "
>  		    "(dev %s sector %llu)\n", page->mapping->host->i_ino,
> -		    start, rcu_str_deref(dev->name), sector);
> +		    start, rcu_string_dereference(dev->name), sector);
>  
>  	bio_put(bio);
>  	return 0;
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 8a8e298..9d4cd72 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -44,6 +44,7 @@
>  #include <linux/uuid.h>
>  #include <linux/btrfs.h>
>  #include <linux/uaccess.h>
> +#include <linux/rcustring.h>
>  #include "ctree.h"
>  #include "disk-io.h"
>  #include "transaction.h"
> @@ -53,7 +54,6 @@
>  #include "locking.h"
>  #include "inode-map.h"
>  #include "backref.h"
> -#include "rcu-string.h"
>  #include "send.h"
>  #include "dev-replace.h"
>  #include "props.h"
> @@ -1583,7 +1583,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
>  	new_size *= root->sectorsize;
>  
>  	printk_in_rcu(KERN_INFO "BTRFS: new size for %s is %llu\n",
> -		      rcu_str_deref(device->name), new_size);
> +		      rcu_string_dereference(device->name), new_size);
>  
>  	if (new_size > old_size) {
>  		trans = btrfs_start_transaction(root, 0);
> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> index 0a6b6e4..eecf738 100644
> --- a/fs/btrfs/raid56.c
> +++ b/fs/btrfs/raid56.c
> @@ -32,6 +32,7 @@
>  #include <linux/list_sort.h>
>  #include <linux/raid/xor.h>
>  #include <linux/vmalloc.h>
> +#include <linux/rcustring.h>
>  #include <asm/div64.h>
>  #include "ctree.h"
>  #include "extent_map.h"
> @@ -42,7 +43,6 @@
>  #include "raid56.h"
>  #include "async-thread.h"
>  #include "check-integrity.h"
> -#include "rcu-string.h"
>  
>  /* set when additional merges to this rbio are not allowed */
>  #define RBIO_RMW_LOCKED_BIT	1
> diff --git a/fs/btrfs/rcu-string.h b/fs/btrfs/rcu-string.h
> deleted file mode 100644
> index 9e111e4..0000000
> --- a/fs/btrfs/rcu-string.h
> +++ /dev/null
> @@ -1,56 +0,0 @@
> -/*
> - * Copyright (C) 2012 Red Hat.  All rights reserved.
> - *
> - * This program is free software; you can redistribute it and/or
> - * modify it under the terms of the GNU General Public
> - * License v2 as published by the Free Software Foundation.
> - *
> - * This program is distributed in the hope that it will be useful,
> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> - * General Public License for more details.
> - *
> - * You should have received a copy of the GNU General Public
> - * License along with this program; if not, write to the
> - * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
> - * Boston, MA 021110-1307, USA.
> - */
> -
> -struct rcu_string {
> -	struct rcu_head rcu;
> -	char str[0];
> -};
> -
> -static inline struct rcu_string *rcu_string_strdup(const char *src, gfp_t mask)
> -{
> -	size_t len = strlen(src) + 1;
> -	struct rcu_string *ret = kzalloc(sizeof(struct rcu_string) +
> -					 (len * sizeof(char)), mask);
> -	if (!ret)
> -		return ret;
> -	strncpy(ret->str, src, len);
> -	return ret;
> -}
> -
> -static inline void rcu_string_free(struct rcu_string *str)
> -{
> -	if (str)
> -		kfree_rcu(str, rcu);
> -}
> -
> -#define printk_in_rcu(fmt, ...) do {	\
> -	rcu_read_lock();		\
> -	printk(fmt, __VA_ARGS__);	\
> -	rcu_read_unlock();		\
> -} while (0)
> -
> -#define printk_ratelimited_in_rcu(fmt, ...) do {	\
> -	rcu_read_lock();				\
> -	printk_ratelimited(fmt, __VA_ARGS__);		\
> -	rcu_read_unlock();				\
> -} while (0)
> -
> -#define rcu_str_deref(rcu_str) ({				\
> -	struct rcu_string *__str = rcu_dereference(rcu_str);	\
> -	__str->str;						\
> -})
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index f4a41f3..62e335f 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -18,6 +18,7 @@
>  
>  #include <linux/blkdev.h>
>  #include <linux/ratelimit.h>
> +#include <linux/rcustring.h>
>  #include "ctree.h"
>  #include "volumes.h"
>  #include "disk-io.h"
> @@ -27,7 +28,6 @@
>  #include "extent_io.h"
>  #include "dev-replace.h"
>  #include "check-integrity.h"
> -#include "rcu-string.h"
>  #include "raid56.h"
>  
>  /*
> @@ -519,7 +519,8 @@ static int scrub_print_warning_inode(u64 inum, u64 offset, u64 root,
>  		printk_in_rcu(KERN_WARNING "BTRFS: %s at logical %llu on dev "
>  			"%s, sector %llu, root %llu, inode %llu, offset %llu, "
>  			"length %llu, links %u (path: %s)\n", swarn->errstr,
> -			swarn->logical, rcu_str_deref(swarn->dev->name),
> +			swarn->logical,
> +			rcu_string_dereference(swarn->dev->name),
>  			(unsigned long long)swarn->sector, root, inum, offset,
>  			min(isize - offset, (u64)PAGE_SIZE), nlink,
>  			(char *)(unsigned long)ipath->fspath->val[i]);
> @@ -531,7 +532,7 @@ err:
>  	printk_in_rcu(KERN_WARNING "BTRFS: %s at logical %llu on dev "
>  		"%s, sector %llu, root %llu, inode %llu, offset %llu: path "
>  		"resolving failed with ret=%d\n", swarn->errstr,
> -		swarn->logical, rcu_str_deref(swarn->dev->name),
> +		swarn->logical, rcu_string_dereference(swarn->dev->name),
>  		(unsigned long long)swarn->sector, root, inum, offset, ret);
>  
>  	free_ipath(ipath);
> @@ -595,7 +596,7 @@ static void scrub_print_warning(const char *errstr, struct scrub_block *sblock)
>  				"BTRFS: %s at logical %llu on dev %s, "
>  				"sector %llu: metadata %s (level %d) in tree "
>  				"%llu\n", errstr, swarn.logical,
> -				rcu_str_deref(dev->name),
> +				rcu_string_dereference(dev->name),
>  				(unsigned long long)swarn.sector,
>  				ref_level ? "node" : "leaf",
>  				ret < 0 ? -1 : ref_level,
> @@ -796,7 +797,7 @@ out:
>  			num_uncorrectable_read_errors);
>  		printk_ratelimited_in_rcu(KERN_ERR "BTRFS: "
>  		    "unable to fixup (nodatasum) error at logical %llu on dev %s\n",
> -			fixup->logical, rcu_str_deref(fixup->dev->name));
> +		    fixup->logical, rcu_string_dereference(fixup->dev->name));
>  	}
>  
>  	btrfs_free_path(path);
> @@ -1198,7 +1199,7 @@ corrected_error:
>  			spin_unlock(&sctx->stat_lock);
>  			printk_ratelimited_in_rcu(KERN_ERR
>  				"BTRFS: fixed up error at logical %llu on dev %s\n",
> -				logical, rcu_str_deref(dev->name));
> +				logical, rcu_string_dereference(dev->name));
>  		}
>  	} else {
>  did_not_correct_error:
> @@ -1207,7 +1208,7 @@ did_not_correct_error:
>  		spin_unlock(&sctx->stat_lock);
>  		printk_ratelimited_in_rcu(KERN_ERR
>  			"BTRFS: unable to fixup (regular) error at logical %llu on dev %s\n",
> -			logical, rcu_str_deref(dev->name));
> +			logical, rcu_string_dereference(dev->name));
>  	}
>  
>  out:
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index c4124de..cf4db62 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -42,6 +42,7 @@
>  #include <linux/cleancache.h>
>  #include <linux/ratelimit.h>
>  #include <linux/btrfs.h>
> +#include <linux/rcustring.h>
>  #include "delayed-inode.h"
>  #include "ctree.h"
>  #include "disk-io.h"
> @@ -54,7 +55,6 @@
>  #include "volumes.h"
>  #include "export.h"
>  #include "compression.h"
> -#include "rcu-string.h"
>  #include "dev-replace.h"
>  #include "free-space-cache.h"
>  #include "backref.h"
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 340a92d..8b1e5e8 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -27,6 +27,7 @@
>  #include <linux/kthread.h>
>  #include <linux/raid/pq.h>
>  #include <linux/semaphore.h>
> +#include <linux/rcustring.h>
>  #include <asm/div64.h>
>  #include "ctree.h"
>  #include "extent_map.h"
> @@ -37,7 +38,6 @@
>  #include "raid56.h"
>  #include "async-thread.h"
>  #include "check-integrity.h"
> -#include "rcu-string.h"
>  #include "math.h"
>  #include "dev-replace.h"
>  #include "sysfs.h"
> @@ -6323,7 +6323,7 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
>  	if (ret < 0) {
>  		printk_in_rcu(KERN_WARNING "BTRFS: "
>  			"error %d while searching for dev_stats item for device %s!\n",
> -			      ret, rcu_str_deref(device->name));
> +			      ret, rcu_string_dereference(device->name));
>  		goto out;
>  	}
>  
> @@ -6334,7 +6334,7 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
>  		if (ret != 0) {
>  			printk_in_rcu(KERN_WARNING "BTRFS: "
>  				"delete too small dev_stats item for device %s failed %d!\n",
> -				      rcu_str_deref(device->name), ret);
> +				rcu_string_dereference(device->name), ret);
>  			goto out;
>  		}
>  		ret = 1;
> @@ -6347,8 +6347,8 @@ static int update_dev_stat_item(struct btrfs_trans_handle *trans,
>  					      &key, sizeof(*ptr));
>  		if (ret < 0) {
>  			printk_in_rcu(KERN_WARNING "BTRFS: "
> -					  "insert dev_stats item for device %s failed %d!\n",
> -				      rcu_str_deref(device->name), ret);
> +				      "insert dev_stats item for device %s failed %d!\n",
> +				      rcu_string_dereference(device->name), ret);
>  			goto out;
>  		}
>  	}
> @@ -6402,7 +6402,7 @@ static void btrfs_dev_stat_print_on_error(struct btrfs_device *dev)
>  		return;
>  	printk_ratelimited_in_rcu(KERN_ERR "BTRFS: "
>  			   "bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u\n",
> -			   rcu_str_deref(dev->name),
> +			   rcu_string_dereference(dev->name),
>  			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
>  			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
>  			   btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
> @@ -6422,7 +6422,7 @@ static void btrfs_dev_stat_print_on_load(struct btrfs_device *dev)
>  
>  	printk_in_rcu(KERN_INFO "BTRFS: "
>  		   "bdev %s errs: wr %u, rd %u, flush %u, corrupt %u, gen %u\n",
> -	       rcu_str_deref(dev->name),
> +	       rcu_string_dereference(dev->name),
>  	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_WRITE_ERRS),
>  	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_READ_ERRS),
>  	       btrfs_dev_stat_read(dev, BTRFS_DEV_STAT_FLUSH_ERRS),
> diff --git a/include/linux/rcustring.h b/include/linux/rcustring.h
> new file mode 100644
> index 0000000..18980e9
> --- /dev/null
> +++ b/include/linux/rcustring.h
> @@ -0,0 +1,91 @@
> +/*
> + * RCU-friendly strings
> + *
> + * Copyright (C) 2012 Red Hat.  All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, you can access it online at
> + * http://www.gnu.org/licenses/gpl-2.0.html.
> + */
> +
> +#ifndef _LINUX_RCUSTRING_H
> +#define _LINUX_RCUSTRING_H
> +
> +struct rcu_string {
> +	struct rcu_head rcu;
> +	char str[0];
> +};
> +
> +/**
> + * rcu_string_strdup() - create an RCU string from a string
> + * @src: The string to copy
> + * @flags: Flags for kmalloc
> + */
> +static inline struct rcu_string *rcu_string_strdup(const char *src, gfp_t flags)
> +{
> +	struct rcu_string *ret;
> +	size_t len = strlen(src) + 1;
> +
> +	ret = kmalloc(sizeof(struct rcu_string) + (len * sizeof(char)), flags);
> +	if (!ret)
> +		return ret;
> +	memcpy(ret->str, src, len);
> +	return ret;
> +}
> +
> +/**
> + * rcu_string_free() - free an RCU string
> + * @str: The string
> + */
> +static inline void rcu_string_free(struct rcu_string *str)
> +{
> +	if (str)
> +		kfree_rcu(str, rcu);
> +}
> +
> +/*
> + * rcu_string_dereference() - dereference an RCU string
> + * @str: The string
> + *
> + * Like rcu_dereference, this must be done in an RCU critical section.
> + */
> +static inline char *rcu_string_dereference(struct rcu_string *rcu_str)
> +{
> +	return rcu_dereference(rcu_str)->str;
> +}
> +
> +/**
> + * printk_in_rcu() - printk in an RCU read-side critical section
> + */
> +#define printk_in_rcu(fmt, ...)			\
> +({						\
> +	int __ret;				\
> +	rcu_read_lock();			\
> +	__ret = printk(fmt, __VA_ARGS__);	\
> +	rcu_read_unlock();			\
> +	__ret;					\
> +})
> +
> +/**
> + * printk_ratelimited_in_rcu() - printk in an RCU read-side critical section
> + */
> +#define printk_ratelimited_in_rcu(fmt, ...)		\
> +({							\
> +	int __ret;					\
> +	rcu_read_lock();				\
> +	__ret = printk_ratelimited(fmt, __VA_ARGS__);	\
> +	rcu_read_unlock();				\
> +	__ret;						\
> +})
> +
> +#endif
> -- 
> 2.1.0
>