Dear John,
Thank you for your patch.
I’d recommend, to use a statement in the git commit message/summary by
adding a verb (in imperative mood). Maybe:
Fix panic during XDP_TX with > 64 CPUs
Am 08.03.23 um 23:07 schrieb John Hickey:
In commit 'ixgbe: let the xdpdrv work with more than 64 cpus'
(4fe815850bdc), support was added to allow XDP programs to run on systems
I think it’s more common to write it like:
In commit 4fe815850bdc (ixgbe: let the xdpdrv work with more than 64 cpus) …
Even shorter
Commit 4fe815850bdc (ixgbe: let the xdpdrv work with more than 64 cpus)
adds support to allow XDP programs …
with more than 64 CPUs by locking the XDP TX rings and indexing them
using cpu % 64 (IXGBE_MAX_XDP_QS).
Upon trying this out patch via the Intel 5.18.6 out of tree driver
Upon trying this patch out via …
on a system with more than 64 cores, the kernel paniced with an
array-index-out-of-bounds at the return in ixgbe_determine_xdp_ring in
ixgbe.h, which means ixgbe_determine_xdp_q_idx was just returning the
cpu instead of cpu % IXGBE_MAX_XDP_QS. An example splat:
Please add, that you have UBSAN enabled, or does it happen without?
==========================================================================
UBSAN: array-index-out-of-bounds in
/var/lib/dkms/ixgbe/5.18.6+focal-1/build/src/ixgbe.h:1147:26
index 65 is out of range for type 'ixgbe_ring *[64]'
==========================================================================
BUG: kernel NULL pointer dereference, address: 0000000000000058
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 65 PID: 408 Comm: ksoftirqd/65
Tainted: G IOE 5.15.0-48-generic #54~20.04.1-Ubuntu
Hardware name: Dell Inc. PowerEdge R640/0W23H8, BIOS 2.5.4 01/13/2020
RIP: 0010:ixgbe_xmit_xdp_ring+0x1b/0x1c0 [ixgbe]
Code: 3b 52 d4 cf e9 42 f2 ff ff 66 0f 1f 44 00 00 0f 1f 44 00 00 55 b9
00 00 00 00 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 ec 08 <44> 0f b7
47 58 0f b7 47 5a 0f b7 57 54 44 0f b7 76 08 66 41 39 c0
If you do not it yet, `scripts/decode_stacktrace.sh` helps decoding
these traces.
RSP: 0018:ffffbc3fcd88fcb0 EFLAGS: 00010282
RAX: ffff92a253260980 RBX: ffffbc3fe68b00a0 RCX: 0000000000000000
RDX: ffff928b5f659000 RSI: ffff928b5f659000 RDI: 0000000000000000
RBP: ffffbc3fcd88fce0 R08: ffff92b9dfc20580 R09: 0000000000000001
R10: 3d3d3d3d3d3d3d3d R11: 3d3d3d3d3d3d3d3d R12: 0000000000000000
R13: ffff928b2f0fa8c0 R14: ffff928b9be20050 R15: 000000000000003c
FS: 0000000000000000(0000) GS:ffff92b9dfc00000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000058 CR3: 000000011dd6a002 CR4: 00000000007706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
<TASK>
ixgbe_poll+0x103e/0x1280 [ixgbe]
? sched_clock_cpu+0x12/0xe0
__napi_poll+0x30/0x160
net_rx_action+0x11c/0x270
__do_softirq+0xda/0x2ee
run_ksoftirqd+0x2f/0x50
smpboot_thread_fn+0xb7/0x150
? sort_range+0x30/0x30
kthread+0x127/0x150
? set_kthread_struct+0x50/0x50
ret_from_fork+0x1f/0x30
</TASK>
I think this is how it happens:
Upon loading the first XDP program on a system with more than 64 CPUs,
ixgbe_xdp_locking_key is incremented in ixgbe_xdp_setup. However,
immediately after this, the rings are reconfigured by ixgbe_setup_tc.
ixgbe_setup_tc calls ixgbe_clear_interrupt_scheme which calls
ixgbe_free_q_vectors which calls ixgbe_free_q_vector in a loop.
ixgbe_free_q_vector decrements ixgbe_xdp_locking_key once per call if
it is non-zero. Commenting out the decrement in ixgbe_free_q_vector
stopped my system from panicing.
I suspect to make the original patch work, I would need to load an XDP
program and then replace it in order to get ixgbe_xdp_locking_key back
above 0 since ixgbe_setup_tc is only called when transitioning between
XDP and non-XDP ring configurations, while ixgbe_xdp_locking_key is
incremented every time ixgbe_xdp_setup is called.
Also, ixgbe_setup_tc can be called via ethtool --set-channels, so this
becomes another path to decrement ixgbe_xdp_locking_key to 0 on systems
with greater than 64 CPUs.
… with more than 64 CPUs.
For this patch, I have changed static_branch_inc to static_branch_enable
in ixgbe_setup_xdp. We weren't counting references. The
ixgbe_xdp_locking_key only protects code in the XDP_TX path, which is
not run when an XDP program is loaded. The other condition for setting
it on is the number of CPUs, which I assume is static.
Fixes: 4fe815850bdc ("ixgbe: let the xdpdrv work with more than 64 cpus")
Signed-off-by: John Hickey <jjh@xxxxxxxxxxxx>
---
v1 -> v2:
Added Fixes and net tag. No code changes.
v2 -> v3:
Added splat. Slight clarification as to why ixgbe_xdp_locking_key
is not turned off. Based on feedback from Maciej Fijalkowski.
---
drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c | 3 ---
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 2 +-
2 files changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c
index f8156fe4b1dc..0ee943db3dc9 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c
@@ -1035,9 +1035,6 @@ static void ixgbe_free_q_vector(struct ixgbe_adapter *adapter, int v_idx)
adapter->q_vector[v_idx] = NULL;
__netif_napi_del(&q_vector->napi);
- if (static_key_enabled(&ixgbe_xdp_locking_key))
- static_branch_dec(&ixgbe_xdp_locking_key);
-
/*
* after a call to __netif_napi_del() napi may still be used and
* ixgbe_get_stats64() might access the rings on this vector,
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index ab8370c413f3..cd2fb72c67be 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -10283,7 +10283,7 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
if (nr_cpu_ids > IXGBE_MAX_XDP_QS * 2)
return -ENOMEM;
else if (nr_cpu_ids > IXGBE_MAX_XDP_QS)
- static_branch_inc(&ixgbe_xdp_locking_key);
+ static_branch_enable(&ixgbe_xdp_locking_key);
old_prog = xchg(&adapter->xdp_prog, prog);
need_reset = (!!prog != !!old_prog);
Kind regards,
Paul
