2023-07-25 20:37:45

by Arnd Bergmann

Subject: [PATCH] [v2] bpf: work around -Wuninitialized warning

From: Arnd Bergmann <[email protected]>

Splitting these out into separate helper functions means that we
actually pass an uninitialized variable into another function call
if dec_active() happens to not be inlined, and CONFIG_PREEMPT_RT
is disabled:

kernel/bpf/memalloc.c: In function 'add_obj_to_free_list':
kernel/bpf/memalloc.c:200:9: error: 'flags' is used uninitialized [-Werror=uninitialized]
200 | dec_active(c, flags);

Avoid this by passing the flags by reference, so they either get
initialized and dereferenced through a pointer, or the pointer never
gets accessed at all.

Fixes: 18e027b1c7c6d ("bpf: Factor out inc/dec of active flag into helpers.")
Suggested-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
---
kernel/bpf/memalloc.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 51d6389e5152e..14d9b1a9a4cac 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -183,11 +183,11 @@ static void inc_active(struct bpf_mem_cache *c, unsigned long *flags)
WARN_ON_ONCE(local_inc_return(&c->active) != 1);
}

-static void dec_active(struct bpf_mem_cache *c, unsigned long flags)
+static void dec_active(struct bpf_mem_cache *c, unsigned long *flags)
{
local_dec(&c->active);
if (IS_ENABLED(CONFIG_PREEMPT_RT))
- local_irq_restore(flags);
+ local_irq_restore(*flags);
}

static void add_obj_to_free_list(struct bpf_mem_cache *c, void *obj)
@@ -197,7 +197,7 @@ static void add_obj_to_free_list(struct bpf_mem_cache *c, void *obj)
inc_active(c, &flags);
__llist_add(obj, &c->free_llist);
c->free_cnt++;
- dec_active(c, flags);
+ dec_active(c, &flags);
}

/* Mostly runs from irq_work except __init phase. */
@@ -344,7 +344,7 @@ static void free_bulk(struct bpf_mem_cache *c)
cnt = --c->free_cnt;
else
cnt = 0;
- dec_active(c, flags);
+ dec_active(c, &flags);
if (llnode)
enque_to_free(tgt, llnode);
} while (cnt > (c->high_watermark + c->low_watermark) / 2);
@@ -384,7 +384,7 @@ static void check_free_by_rcu(struct bpf_mem_cache *c)
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu))
if (__llist_add(llnode, &c->free_by_rcu))
c->free_by_rcu_tail = llnode;
- dec_active(c, flags);
+ dec_active(c, &flags);
}

if (llist_empty(&c->free_by_rcu))
@@ -408,7 +408,7 @@ static void check_free_by_rcu(struct bpf_mem_cache *c)
inc_active(c, &flags);
WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu));
c->waiting_for_gp_tail = c->free_by_rcu_tail;
- dec_active(c, flags);
+ dec_active(c, &flags);

if (unlikely(READ_ONCE(c->draining))) {
free_all(llist_del_all(&c->waiting_for_gp), !!c->percpu_size);
--
2.39.2

2023-07-26 00:56:08

by patchwork-bot+netdevbpf

Subject: Re: [PATCH] [v2] bpf: work around -Wuninitialized warning

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[email protected]>:

On Tue, 25 Jul 2023 22:26:40 +0200 you wrote:
> From: Arnd Bergmann <[email protected]>
>
> Splitting these out into separate helper functions means that we
> actually pass an uninitialized variable into another function call
> if dec_active() happens to not be inlined, and CONFIG_PREEMPT_RT
> is disabled:
>
> [...]

Here is the summary with links:
- [v2] bpf: work around -Wuninitialized warning
https://git.kernel.org/bpf/bpf-next/c/63e2da3b7f7f

You are awesome, thank you!
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