Re: [PATCH bpf-next v2 1/3] bpf, sockmap: avoid using sk_socket after free

[Michal Luczaj]

On 3/10/25 12:36, Jiayuan Chen wrote:
> March 7, 2025 at 5:45 PM, "Michal Luczaj" <mhal@xxxxxxx> wrote:
> ...
>> BTW, lockdep (CONFIG_LOCKDEP=y) complains about calling AF_UNIX's
>> read_skb() under RCU read lock.
>>
> My environment also has LOCKDEP enabled, but I didn't see similar
> warnings.
> Moreover, RCU assertions are typically written as:
> 
> WARN_ON_ONCE(!rcu_read_lock_held())
> 
> And when LOCKDEP is not enabled, rcu_read_lock_held() defaults to
> returning 1. So, it's unlikely to trigger a warning due to an RCU lock
> being held.
> 
> Could you provide more of the call stack?

Sure, bpf-next with this series applied, test_progs -t sockmap_basic:

=============================
[ BUG: Invalid wait context ]
6.14.0-rc3+ #111 Tainted: G           OE
-----------------------------
test_progs/37755 is trying to lock:
ffff88810d9bc3c0 (&u->iolock){+.+.}-{4:4}, at: unix_stream_read_skb+0x30/0x120
other info that might help us debug this:
context-{5:5}
1 lock held by test_progs/37755:
 #0: ffffffff833700e0 (rcu_read_lock){....}-{1:3}, at: sk_psock_verdict_data_ready+0x3e/0x2a0
stack backtrace:
CPU: 13 UID: 0 PID: 37755 Comm: test_progs Tainted: G           OE      6.14.0-rc3+ #111
Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
Call Trace:
 dump_stack_lvl+0x68/0x90
 lock_acquire+0xcf/0x2e0
 __mutex_lock+0x9c/0xcc0
 unix_stream_read_skb+0x30/0x120
 sk_psock_verdict_data_ready+0x8d/0x2a0
 unix_stream_sendmsg+0x232/0x640
 __sys_sendto+0x1cd/0x1e0
 __x64_sys_sendto+0x20/0x30
 do_syscall_64+0x93/0x180
 entry_SYSCALL_64_after_hwframe+0x76/0x7e