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Subject[PATCH 5.4 64/65] net: sched: replaced invalid qdisc tree flush helper in qdisc_replace
Date
From: Alexander Ovechkin <ovov@yandex-team.ru>

commit 938e0fcd3253efdef8924714158911286d08cfe1 upstream.

Commit e5f0e8f8e456 ("net: sched: introduce and use qdisc tree flush/purge helpers")
introduced qdisc tree flush/purge helpers, but erroneously used flush helper
instead of purge helper in qdisc_replace function.
This issue was found in our CI, that tests various qdisc setups by configuring
qdisc and sending data through it. Call of invalid helper sporadically leads
to corruption of vt_tree/cf_tree of hfsc_class that causes kernel oops:

Oops: 0000 [#1] SMP PTI
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.11.0-8f6859df #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014
RIP: 0010:rb_insert_color+0x18/0x190
Code: c3 31 c0 c3 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 48 8b 07 48 85 c0 0f 84 05 01 00 00 48 8b 10 f6 c2 01 0f 85 34 01 00 00 <48> 8b 4a 08 49 89 d0 48 39 c1 74 7d 48 85 c9 74 32 f6 01 01 75 2d
RSP: 0018:ffffc900000b8bb0 EFLAGS: 00010246
RAX: ffff8881ef4c38b0 RBX: ffff8881d956e400 RCX: ffff8881ef4c38b0
RDX: 0000000000000000 RSI: ffff8881d956f0a8 RDI: ffff8881d956e4b0
RBP: 0000000000000000 R08: 000000d5c4e249da R09: 1600000000000000
R10: ffffc900000b8be0 R11: ffffc900000b8b28 R12: 0000000000000001
R13: 000000000000005a R14: ffff8881f0905000 R15: ffff8881f0387d00
FS: 0000000000000000(0000) GS:ffff8881f8b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000008 CR3: 00000001f4796004 CR4: 0000000000060ee0
Call Trace:
<IRQ>
init_vf.isra.19+0xec/0x250 [sch_hfsc]
hfsc_enqueue+0x245/0x300 [sch_hfsc]
? fib_rules_lookup+0x12a/0x1d0
? __dev_queue_xmit+0x4b6/0x930
? hfsc_delete_class+0x250/0x250 [sch_hfsc]
__dev_queue_xmit+0x4b6/0x930
? ip6_finish_output2+0x24d/0x590
ip6_finish_output2+0x24d/0x590
? ip6_output+0x6c/0x130
ip6_output+0x6c/0x130
? __ip6_finish_output+0x110/0x110
mld_sendpack+0x224/0x230
mld_ifc_timer_expire+0x186/0x2c0
? igmp6_group_dropped+0x200/0x200
call_timer_fn+0x2d/0x150
run_timer_softirq+0x20c/0x480
? tick_sched_do_timer+0x60/0x60
? tick_sched_timer+0x37/0x70
__do_softirq+0xf7/0x2cb
irq_exit+0xa0/0xb0
smp_apic_timer_interrupt+0x74/0x150
apic_timer_interrupt+0xf/0x20
</IRQ>

Fixes: e5f0e8f8e456 ("net: sched: introduce and use qdisc tree flush/purge helpers")
Signed-off-by: Alexander Ovechkin <ovov@yandex-team.ru>
Reported-by: Alexander Kuznetsov <wwfq@yandex-team.ru>
Acked-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Acked-by: Dmitry Yakunin <zeil@yandex-team.ru>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Link: https://lore.kernel.org/r/20210201200049.299153-1-ovov@yandex-team.ru
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/sch_generic.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -1158,7 +1158,7 @@ static inline struct Qdisc *qdisc_replac
old = *pold;
*pold = new;
if (old != NULL)
- qdisc_tree_flush_backlog(old);
+ qdisc_purge_queue(old);
sch_tree_unlock(sch);

return old;

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