Re: [PATCH net] Revert "net: phy: Correctly process PHY_HALTED in phy_stop_machine()"

[David Miller <davem@davemloft.net>]

From: Florian Fainelli <f.fainelli@gmail.com>
Date: Wed, 30 Aug 2017 17:49:29 -0700

> This reverts commit 7ad813f208533cebfcc32d3d7474dc1677d1b09a ("net: phy:
> Correctly process PHY_HALTED in phy_stop_machine()") because it is
> creating the possibility for a NULL pointer dereference.
> 
> David Daney provide the following call trace and diagram of events:
> 
> When ndo_stop() is called we call:
> 
>  phy_disconnect()
>     +---> phy_stop_interrupts() implies: phydev->irq = PHY_POLL;
>     +---> phy_stop_machine()
>     |      +---> phy_state_machine()
>     |              +----> queue_delayed_work(): Work queued.
>     +--->phy_detach() implies: phydev->attached_dev = NULL;
> 
> Now at a later time the queued work does:
> 
>  phy_state_machine()
>     +---->netif_carrier_off(phydev->attached_dev): Oh no! It is NULL:
> 
>  CPU 12 Unable to handle kernel paging request at virtual address
> 0000000000000048, epc == ffffffff80de37ec, ra == ffffffff80c7c
> Oops[#1]:
> CPU: 12 PID: 1502 Comm: kworker/12:1 Not tainted 4.9.43-Cavium-Octeon+ #1
> Workqueue: events_power_efficient phy_state_machine
> task: 80000004021ed100 task.stack: 8000000409d70000
> $ 0   : 0000000000000000 ffffffff84720060 0000000000000048 0000000000000004
> $ 4   : 0000000000000000 0000000000000001 0000000000000004 0000000000000000
> $ 8   : 0000000000000000 0000000000000000 00000000ffff98f3 0000000000000000
> $12   : 8000000409d73fe0 0000000000009c00 ffffffff846547c8 000000000000af3b
> $16   : 80000004096bab68 80000004096babd0 0000000000000000 80000004096ba800
> $20   : 0000000000000000 0000000000000000 ffffffff81090000 0000000000000008
> $24   : 0000000000000061 ffffffff808637b0
> $28   : 8000000409d70000 8000000409d73cf0 80000000271bd300 ffffffff80c7804c
> Hi    : 000000000000002a
> Lo    : 000000000000003f
> epc   : ffffffff80de37ec netif_carrier_off+0xc/0x58
> ra    : ffffffff80c7804c phy_state_machine+0x48c/0x4f8
> Status: 14009ce3        KX SX UX KERNEL EXL IE
> Cause : 00800008 (ExcCode 02)
> BadVA : 0000000000000048
> PrId  : 000d9501 (Cavium Octeon III)
> Modules linked in:
> Process kworker/12:1 (pid: 1502, threadinfo=8000000409d70000,
> task=80000004021ed100, tls=0000000000000000)
> Stack : 8000000409a54000 80000004096bab68 80000000271bd300 80000000271c1e00
>         0000000000000000 ffffffff808a1708 8000000409a54000 80000000271bd300
>         80000000271bd320 8000000409a54030 ffffffff80ff0f00 0000000000000001
>         ffffffff81090000 ffffffff808a1ac0 8000000402182080 ffffffff84650000
>         8000000402182080 ffffffff84650000 ffffffff80ff0000 8000000409a54000
>         ffffffff808a1970 0000000000000000 80000004099e8000 8000000402099240
>         0000000000000000 ffffffff808a8598 0000000000000000 8000000408eeeb00
>         8000000409a54000 00000000810a1d00 0000000000000000 8000000409d73de8
>         8000000409d73de8 0000000000000088 000000000c009c00 8000000409d73e08
>         8000000409d73e08 8000000402182080 ffffffff808a84d0 8000000402182080
>         ...
> Call Trace:
> [<ffffffff80de37ec>] netif_carrier_off+0xc/0x58
> [<ffffffff80c7804c>] phy_state_machine+0x48c/0x4f8
> [<ffffffff808a1708>] process_one_work+0x158/0x368
> [<ffffffff808a1ac0>] worker_thread+0x150/0x4c0
> [<ffffffff808a8598>] kthread+0xc8/0xe0
> [<ffffffff808617f0>] ret_from_kernel_thread+0x14/0x1c
> 
> The original motivation for this change originated from Marc Gonzales
> indicating that his network driver did not have its adjust_link callback
> executing with phydev->link = 0 while he was expecting it.
> 
> PHYLIB has never made any such guarantees ever because phy_stop() merely just
> tells the workqueue to move into PHY_HALTED state which will happen
> asynchronously.
> 
> Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
> Reported-by: David Daney <ddaney.cavm@gmail.com>
> Fixes: 7ad813f20853 ("net: phy: Correctly process PHY_HALTED in phy_stop_machine()")
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

Applied and queued up for -stable, thanks Florian.