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SubjectRe: [PATCH 1/1] Drivers: hv: vmbus: Fix rescind handling issues
Date
Vitaly Kuznetsov <vkuznets@redhat.com> writes:

>
> Reverting 6f3d791f300618caf82a2be0c27456edd76d5164 still helps.

In addition to the above I got the following crash while playing with
4.14-rc1 (unmodified):

[ 55.810080] kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
[ 55.814293] BUG: unable to handle kernel paging request at ffff8800059985f0
[ 55.818065] IP: 0xffff8800059985f0
[ 55.819925] PGD 22eb067 P4D 22eb067 PUD 22ec067 PMD 5f37063 PTE 8000000005998163
[ 55.820018] Oops: 0011 [#1] SMP
[ 55.820018] Modules linked in: vfat fat bnx2x mdio efi_pstore hv_utils efivars pci_hyperv ptp pps_core pcspkr hv_balloon xfs libcrc32c hv_storvsc hyperv_fb hv_netvsc scsi_transport_fc hid_hyperv hyperv_keyboard hv_vmbus
[ 55.834837] CPU: 0 PID: 498 Comm: kworker/0:2 Not tainted 4.14.0-rc1 #63
[ 55.834837] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v1.0 11/26/2012
[ 55.834837] Workqueue: events vmbus_onmessage_work [hv_vmbus]
[ 55.834837] task: ffff88003f448000 task.stack: ffffc90005398000
[ 55.834837] RIP: 0010:0xffff8800059985f0
[ 55.834837] RSP: 0018:ffffc9000539be00 EFLAGS: 00010286
[ 55.834837] RAX: ffff880005998010 RBX: ffff880005998000 RCX: 0000000000000000
[ 55.834837] RDX: ffff8800059985f0 RSI: 0000000000000246 RDI: ffff880005998000
[ 55.860040] RBP: ffffc9000539be18 R08: 00000000000002e6 R09: 0000000000000000
[ 55.865057] R10: ffffc9000539bdf0 R11: 000000000000a000 R12: 0000000000000286
[ 55.865057] R13: ffff88007ae1ed00 R14: 0000000000000000 R15: ffff8800065c3200
[ 55.865057] FS: 0000000000000000(0000) GS:ffff88007ae00000(0000) knlGS:0000000000000000
[ 55.865057] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 55.865057] CR2: ffff8800059985f0 CR3: 00000000075a5000 CR4: 00000000001406f0
[ 55.886745] Call Trace:
[ 55.886745] ? vmbus_onoffer_rescind+0xfa/0x160 [hv_vmbus]
[ 55.890968] vmbus_onmessage+0x2a/0x90 [hv_vmbus]
[ 55.891934] vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
[ 55.891934] process_one_work+0x193/0x390
[ 55.891934] worker_thread+0x48/0x3c0
[ 55.891934] kthread+0x120/0x140
[ 55.891934] ? process_one_work+0x390/0x390
[ 55.891934] ? kthread_create_on_node+0x60/0x60
[ 55.891934] ret_from_fork+0x25/0x30
[ 55.891934] Code: 88 ff ff c0 85 99 05 00 88 ff ff d0 85 99 05 00 88 ff ff d0 85 99 05 00 88 ff ff e0 85 99 05 00 88 ff ff e0 85 99 05 00 88 ff ff <f0> 85 99 05 00 88 ff ff f0 85 99 05 00 88 ff ff 00 86 99 05 00
[ 55.922505] RIP: 0xffff8800059985f0 RSP: ffffc9000539be00
[ 55.922505] CR2: ffff8800059985f0
[ 55.922505] ---[ end trace 25226e00af3f94fb ]---
[ 55.933590] Kernel panic - not syncing: Fatal exception
[ 55.933590] Kernel Offset: disabled
[ 55.933590] ---[ end Kernel panic - not syncing: Fatal exception

So it seems that during

while (READ_ONCE(channel->probe_done) == false) {
/*
* We wait here until any channel offer is currently
* being processed.
*/
msleep(1);
}

loop the channel disappeared. The issue may not be related to the netvsc
hang I mentioned before. It may make sense to do refcounting for
channels/subchannels (or employ RCU).

--
Vitaly

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