Patch "bpf: Use raw_spinlock_t in ringbuf" has been added to the 6.11-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Use raw_spinlock_t in ringbuf

to the 6.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-use-raw_spinlock_t-in-ringbuf.patch
and it can be found in the queue-6.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6e42950105ee79c8fb3c5042982980302b840177
Author: Wander Lairson Costa <wander.lairson@xxxxxxxxx>
Date:   Fri Sep 20 16:06:59 2024 -0300

    bpf: Use raw_spinlock_t in ringbuf
    
    [ Upstream commit 8b62645b09f870d70c7910e7550289d444239a46 ]
    
    The function __bpf_ringbuf_reserve is invoked from a tracepoint, which
    disables preemption. Using spinlock_t in this context can lead to a
    "sleep in atomic" warning in the RT variant. This issue is illustrated
    in the example below:
    
    BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
    in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 556208, name: test_progs
    preempt_count: 1, expected: 0
    RCU nest depth: 1, expected: 1
    INFO: lockdep is turned off.
    Preemption disabled at:
    [<ffffd33a5c88ea44>] migrate_enable+0xc0/0x39c
    CPU: 7 PID: 556208 Comm: test_progs Tainted: G
    Hardware name: Qualcomm SA8775P Ride (DT)
    Call trace:
     dump_backtrace+0xac/0x130
     show_stack+0x1c/0x30
     dump_stack_lvl+0xac/0xe8
     dump_stack+0x18/0x30
     __might_resched+0x3bc/0x4fc
     rt_spin_lock+0x8c/0x1a4
     __bpf_ringbuf_reserve+0xc4/0x254
     bpf_ringbuf_reserve_dynptr+0x5c/0xdc
     bpf_prog_ac3d15160d62622a_test_read_write+0x104/0x238
     trace_call_bpf+0x238/0x774
     perf_call_bpf_enter.isra.0+0x104/0x194
     perf_syscall_enter+0x2f8/0x510
     trace_sys_enter+0x39c/0x564
     syscall_trace_enter+0x220/0x3c0
     do_el0_svc+0x138/0x1dc
     el0_svc+0x54/0x130
     el0t_64_sync_handler+0x134/0x150
     el0t_64_sync+0x17c/0x180
    
    Switch the spinlock to raw_spinlock_t to avoid this error.
    
    Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it")
    Reported-by: Brian Grech <bgrech@xxxxxxxxxx>
    Signed-off-by: Wander Lairson Costa <wander.lairson@xxxxxxxxx>
    Signed-off-by: Wander Lairson Costa <wander@xxxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240920190700.617253-1-wander@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index e20b90c361316..de3b681d1d13d 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -29,7 +29,7 @@ struct bpf_ringbuf {
 	u64 mask;
 	struct page **pages;
 	int nr_pages;
-	spinlock_t spinlock ____cacheline_aligned_in_smp;
+	raw_spinlock_t spinlock ____cacheline_aligned_in_smp;
 	/* For user-space producer ring buffers, an atomic_t busy bit is used
 	 * to synchronize access to the ring buffers in the kernel, rather than
 	 * the spinlock that is used for kernel-producer ring buffers. This is
@@ -173,7 +173,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
 	if (!rb)
 		return NULL;
 
-	spin_lock_init(&rb->spinlock);
+	raw_spin_lock_init(&rb->spinlock);
 	atomic_set(&rb->busy, 0);
 	init_waitqueue_head(&rb->waitq);
 	init_irq_work(&rb->work, bpf_ringbuf_notify);
@@ -421,10 +421,10 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 	cons_pos = smp_load_acquire(&rb->consumer_pos);
 
 	if (in_nmi()) {
-		if (!spin_trylock_irqsave(&rb->spinlock, flags))
+		if (!raw_spin_trylock_irqsave(&rb->spinlock, flags))
 			return NULL;
 	} else {
-		spin_lock_irqsave(&rb->spinlock, flags);
+		raw_spin_lock_irqsave(&rb->spinlock, flags);
 	}
 
 	pend_pos = rb->pending_pos;
@@ -450,7 +450,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 	 */
 	if (new_prod_pos - cons_pos > rb->mask ||
 	    new_prod_pos - pend_pos > rb->mask) {
-		spin_unlock_irqrestore(&rb->spinlock, flags);
+		raw_spin_unlock_irqrestore(&rb->spinlock, flags);
 		return NULL;
 	}
 
@@ -462,7 +462,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 	/* pairs with consumer's smp_load_acquire() */
 	smp_store_release(&rb->producer_pos, new_prod_pos);
 
-	spin_unlock_irqrestore(&rb->spinlock, flags);
+	raw_spin_unlock_irqrestore(&rb->spinlock, flags);
 
 	return (void *)hdr + BPF_RINGBUF_HDR_SZ;
 }