This is a note to let you know that I've just added the patch titled
net/sched: taprio: avoid disabling offload when it was never enabled
to the 5.10-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:
net-sched-taprio-avoid-disabling-offload-when-it-was.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 19210faea0e6dd691d21545a385b73772e977b4d
Author: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Date: Thu Sep 15 13:08:01 2022 +0300
net/sched: taprio: avoid disabling offload when it was never enabled
[ Upstream commit db46e3a88a09c5cf7e505664d01da7238cd56c92 ]
In an incredibly strange API design decision, qdisc->destroy() gets
called even if qdisc->init() never succeeded, not exclusively since
commit 87b60cfacf9f ("net_sched: fix error recovery at qdisc creation"),
but apparently also earlier (in the case of qdisc_create_dflt()).
The taprio qdisc does not fully acknowledge this when it attempts full
offload, because it starts off with q->flags = TAPRIO_FLAGS_INVALID in
taprio_init(), then it replaces q->flags with TCA_TAPRIO_ATTR_FLAGS
parsed from netlink (in taprio_change(), tail called from taprio_init()).
But in taprio_destroy(), we call taprio_disable_offload(), and this
determines what to do based on FULL_OFFLOAD_IS_ENABLED(q->flags).
But looking at the implementation of FULL_OFFLOAD_IS_ENABLED()
(a bitwise check of bit 1 in q->flags), it is invalid to call this macro
on q->flags when it contains TAPRIO_FLAGS_INVALID, because that is set
to U32_MAX, and therefore FULL_OFFLOAD_IS_ENABLED() will return true on
an invalid set of flags.
As a result, it is possible to crash the kernel if user space forces an
error between setting q->flags = TAPRIO_FLAGS_INVALID, and the calling
of taprio_enable_offload(). This is because drivers do not expect the
offload to be disabled when it was never enabled.
The error that we force here is to attach taprio as a non-root qdisc,
but instead as child of an mqprio root qdisc:
$ tc qdisc add dev swp0 root handle 1: \
mqprio num_tc 8 map 0 1 2 3 4 5 6 7 \
queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 hw 0
$ tc qdisc replace dev swp0 parent 1:1 \
taprio num_tc 8 map 0 1 2 3 4 5 6 7 \
queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 base-time 0 \
sched-entry S 0x7f 990000 sched-entry S 0x80 100000 \
flags 0x0 clockid CLOCK_TAI
Unable to handle kernel paging request at virtual address fffffffffffffff8
[fffffffffffffff8] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 96000004 [#1] PREEMPT SMP
Call trace:
taprio_dump+0x27c/0x310
vsc9959_port_setup_tc+0x1f4/0x460
felix_port_setup_tc+0x24/0x3c
dsa_slave_setup_tc+0x54/0x27c
taprio_disable_offload.isra.0+0x58/0xe0
taprio_destroy+0x80/0x104
qdisc_create+0x240/0x470
tc_modify_qdisc+0x1fc/0x6b0
rtnetlink_rcv_msg+0x12c/0x390
netlink_rcv_skb+0x5c/0x130
rtnetlink_rcv+0x1c/0x2c
Fix this by keeping track of the operations we made, and undo the
offload only if we actually did it.
I've added "bool offloaded" inside a 4 byte hole between "int clockid"
and "atomic64_t picos_per_byte". Now the first cache line looks like
below:
$ pahole -C taprio_sched net/sched/sch_taprio.o
struct taprio_sched {
struct Qdisc * * qdiscs; /* 0 8 */
struct Qdisc * root; /* 8 8 */
u32 flags; /* 16 4 */
enum tk_offsets tk_offset; /* 20 4 */
int clockid; /* 24 4 */
bool offloaded; /* 28 1 */
/* XXX 3 bytes hole, try to pack */
atomic64_t picos_per_byte; /* 32 0 */
/* XXX 8 bytes hole, try to pack */
spinlock_t current_entry_lock; /* 40 0 */
/* XXX 8 bytes hole, try to pack */
struct sched_entry * current_entry; /* 48 8 */
struct sched_gate_list * oper_sched; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
Fixes: 9c66d1564676 ("taprio: Add support for hardware offloading")
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
Reviewed-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index eca525791013..384316c11e98 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -65,6 +65,7 @@ struct taprio_sched {
u32 flags;
enum tk_offsets tk_offset;
int clockid;
+ bool offloaded;
atomic64_t picos_per_byte; /* Using picoseconds because for 10Gbps+
* speeds it's sub-nanoseconds per byte
*/
@@ -1267,6 +1268,8 @@ static int taprio_enable_offload(struct net_device *dev,
goto done;
}
+ q->offloaded = true;
+
done:
taprio_offload_free(offload);
@@ -1281,12 +1284,9 @@ static int taprio_disable_offload(struct net_device *dev,
struct tc_taprio_qopt_offload *offload;
int err;
- if (!FULL_OFFLOAD_IS_ENABLED(q->flags))
+ if (!q->offloaded)
return 0;
- if (!ops->ndo_setup_tc)
- return -EOPNOTSUPP;
-
offload = taprio_offload_alloc(0);
if (!offload) {
NL_SET_ERR_MSG(extack,
@@ -1302,6 +1302,8 @@ static int taprio_disable_offload(struct net_device *dev,
goto out;
}
+ q->offloaded = false;
+
out:
taprio_offload_free(offload);
