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Message-ID: <5pauuhdlh2jaeqixofoips7f4zjl7pcyeykkglkmihsko3cnjy@4cbebl2x3qod>
Date: Mon, 24 Feb 2025 22:04:41 +0800
From: Coly Li <colyli@...nel.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>,
linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 8/8][next] bcache: Avoid -Wflex-array-member-not-at-end
warnings
On Mon, Feb 24, 2025 at 08:31:26PM +0800, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
>
> Change the type of the middle struct members currently causing trouble
> from `struct bio` to `struct bio_hdr`.
>
> We also use `container_of()` whenever we need to retrieve a pointer to
> the flexible structure `struct bio`, through which we can access the
> flexible-array member in it, if necessary.
>
> With these changes fix 112 of the following warnings:
>
> drivers/md/bcache/bcache.h:233:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:241:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:242:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:308:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:422:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/bcache.h:639:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/journal.h:152:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/md/bcache/journal.h:156:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Hi Gustavo,
each struct bio followed by a struct bio_vec at the location where
struct bio is embedded into middle of a structure. So the general
flex-array-in-middle issue doesn't exist here indeed.
I don't suggest to introduce extra complication in bcache code.
How about to improve the checking script, if there is no following
struct bio_vec after struct bio, then that should be something really
suspicious.
Thanks.
Coly Li
> ---
> drivers/md/bcache/bcache.h | 4 ++--
> drivers/md/bcache/journal.c | 10 +++++-----
> drivers/md/bcache/journal.h | 4 ++--
> drivers/md/bcache/super.c | 8 +++++---
> 4 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 785b0d9008fa..328023e90eb2 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -305,7 +305,7 @@ struct cached_dev {
>
> struct cache_sb sb;
> struct cache_sb_disk *sb_disk;
> - struct bio sb_bio;
> + struct bio_hdr sb_bio;
> struct bio_vec sb_bv[1];
> struct closure sb_write;
> struct semaphore sb_write_mutex;
> @@ -419,7 +419,7 @@ struct cache {
> struct cache_set *set;
> struct cache_sb sb;
> struct cache_sb_disk *sb_disk;
> - struct bio sb_bio;
> + struct bio_hdr sb_bio;
> struct bio_vec sb_bv[1];
>
> struct kobject kobj;
> diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
> index 7ff14bd2feb8..2ead129f7758 100644
> --- a/drivers/md/bcache/journal.c
> +++ b/drivers/md/bcache/journal.c
> @@ -36,7 +36,7 @@ static int journal_read_bucket(struct cache *ca, struct list_head *list,
> unsigned int bucket_index)
> {
> struct journal_device *ja = &ca->journal;
> - struct bio *bio = &ja->bio;
> + struct bio *bio = container_of(&ja->bio, struct bio, __hdr);
>
> struct journal_replay *i;
> struct jset *j, *data = ca->set->journal.w[0].data;
> @@ -571,7 +571,7 @@ static void btree_flush_write(struct cache_set *c)
> static void journal_discard_endio(struct bio *bio)
> {
> struct journal_device *ja =
> - container_of(bio, struct journal_device, discard_bio);
> + container_of(&bio->__hdr, struct journal_device, discard_bio);
> struct cache *ca = container_of(ja, struct cache, journal);
>
> atomic_set(&ja->discard_in_flight, DISCARD_DONE);
> @@ -585,13 +585,13 @@ static void journal_discard_work(struct work_struct *work)
> struct journal_device *ja =
> container_of(work, struct journal_device, discard_work);
>
> - submit_bio(&ja->discard_bio);
> + submit_bio(container_of(&ja->discard_bio, struct bio, __hdr));
> }
>
> static void do_journal_discard(struct cache *ca)
> {
> struct journal_device *ja = &ca->journal;
> - struct bio *bio = &ja->discard_bio;
> + struct bio *bio = container_of(&ja->discard_bio, struct bio, __hdr);
>
> if (!ca->discard) {
> ja->discard_idx = ja->last_idx;
> @@ -787,7 +787,7 @@ static CLOSURE_CALLBACK(journal_write_unlocked)
>
> for (i = 0; i < KEY_PTRS(k); i++) {
> ca = c->cache;
> - bio = &ca->journal.bio;
> + bio = container_of(&ca->journal.bio, struct bio, __hdr);
>
> atomic_long_add(sectors, &ca->meta_sectors_written);
>
> diff --git a/drivers/md/bcache/journal.h b/drivers/md/bcache/journal.h
> index cd316b4a1e95..b4ff5269aee3 100644
> --- a/drivers/md/bcache/journal.h
> +++ b/drivers/md/bcache/journal.h
> @@ -149,11 +149,11 @@ struct journal_device {
> atomic_t discard_in_flight;
>
> struct work_struct discard_work;
> - struct bio discard_bio;
> + struct bio_hdr discard_bio;
> struct bio_vec discard_bv;
>
> /* Bio for journal reads/writes to this device */
> - struct bio bio;
> + struct bio_hdr bio;
> struct bio_vec bv[8];
> };
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index e42f1400cea9..cd1342355cf2 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -337,7 +337,7 @@ static CLOSURE_CALLBACK(bch_write_bdev_super_unlock)
> void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent)
> {
> struct closure *cl = &dc->sb_write;
> - struct bio *bio = &dc->sb_bio;
> + struct bio *bio = container_of(&dc->sb_bio, struct bio, __hdr);
>
> down(&dc->sb_write_mutex);
> closure_init(cl, parent);
> @@ -374,7 +374,7 @@ void bcache_write_super(struct cache_set *c)
> {
> struct closure *cl = &c->sb_write;
> struct cache *ca = c->cache;
> - struct bio *bio = &ca->sb_bio;
> + struct bio *bio = container_of(&ca->sb_bio, struct bio, __hdr);
> unsigned int version = BCACHE_SB_VERSION_CDEV_WITH_UUID;
>
> down(&c->sb_write_mutex);
> @@ -2230,7 +2230,9 @@ static int cache_alloc(struct cache *ca)
> __module_get(THIS_MODULE);
> kobject_init(&ca->kobj, &bch_cache_ktype);
>
> - bio_init(&ca->journal.bio, NULL, ca->journal.bio.bi_inline_vecs, 8, 0);
> + bio_init(container_of(&ca->journal.bio, struct bio, __hdr), NULL,
> + container_of(&ca->journal.bio, struct bio, __hdr)->bi_inline_vecs,
> + 8, 0);
>
> /*
> * when ca->sb.njournal_buckets is not zero, journal exists,
> --
> 2.43.0
>
--
Coly Li
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