On Mon, Oct 16, 2017 at 3:32 PM, David Ahern <dsah...@gmail.com> wrote:
> Running perf in one window to capture tcp_retransmit_skb tracepoint:
> $ perf record -e tcp:tcp_retransmit_skb -a
>
> And causing a retransmission on an active TCP session (e.g., dropping
> packets in the receiver, changing MTU on the interface to 500 and back
> to 1500) triggers a panic:
>
> [ 58.543144] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000008
> [ 58.545300] IP: perf_trace_tcp_retransmit_skb+0xd0/0x145
> [ 58.546770] PGD 0 P4D 0
> [ 58.547472] Oops: 0000 [#1] SMP
> [ 58.548328] Modules linked in: vrf
> [ 58.549262] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc4+ #26
> [ 58.551004] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.7.5-20140531_083030-gandalf 04/01/2014
> [ 58.554560] task: ffffffff81a0e540 task.stack: ffffffff81a00000
> [ 58.555817] RIP: 0010:perf_trace_tcp_retransmit_skb+0xd0/0x145
> [ 58.557137] RSP: 0018:ffff88003fc03d68 EFLAGS: 00010282
> [ 58.558292] RAX: 0000000000000000 RBX: ffffe8ffffc0ec80 RCX:
> ffff880038543098
> [ 58.559850] RDX: 0400000000000000 RSI: ffff88003fc03d70 RDI:
> ffff88003fc14b68
> [ 58.561099] RBP: ffff88003fc03da8 R08: 0000000000000000 R09:
> ffffea0000d3224a
> [ 58.562005] R10: ffff88003fc03db8 R11: 0000000000000010 R12:
> ffff8800385428c0
> [ 58.562930] R13: ffffe8ffffc0e478 R14: ffffffff81a93a40 R15:
> ffff88003d4f0c00
> [ 58.563845] FS: 0000000000000000(0000) GS:ffff88003fc00000(0000)
> knlGS:0000000000000000
> [ 58.564873] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 58.565613] CR2: 0000000000000008 CR3: 000000003d68f004 CR4:
> 00000000000606f0
> [ 58.566538] Call Trace:
> [ 58.566865] <IRQ>
> [ 58.567140] __tcp_retransmit_skb+0x4ab/0x4c6
> [ 58.567704] ? tcp_set_ca_state+0x22/0x3f
> [ 58.568231] tcp_retransmit_skb+0x14/0xa3
> [ 58.568754] tcp_retransmit_timer+0x472/0x5e3
> [ 58.569324] ? tcp_write_timer_handler+0x1e9/0x1e9
> [ 58.569946] tcp_write_timer_handler+0x95/0x1e9
> [ 58.570548] tcp_write_timer+0x2a/0x58
>
> Check that daddr_cache is non-NULL before de-referencing.
>
> Fixes: e086101b150a ("tcp: add a tracepoint for tcp retransmission")
> Signed-off-by: David Ahern <dsah...@gmail.com>
Acked-by: Cong Wang <xiyou.wangc...@gmail.com>
