Re: [PATCH v1 1/1] usb: cdc_acm: prevent race at write to acm while system resumes

[Greg KH]

On Mon, Feb 12, 2018 at 12:15:03PM -0800, sathyanarayan.kuppuswamy@xxxxxxxxxxxxxxx wrote:
> From: Dominik Bozek <dominikx.bozek@xxxxxxxxx>
> 
> ACM driver may accept data to transmit while system is not fully
> resumed. In this case ACM driver buffers data and prepare URBs
> on usb anchor list.
> There is a little chance that two tasks put a char and initiate
> acm_tty_flush_chars(). In such a case, driver will put one URB
> twice on usb anchor list.
> This patch also reset length of data before resue of a buffer.
> This not only prevent sending rubbish, but also lower risc of race.
> 
> Without this patch we hit following kernel panic in one of our
> stabilty/stress tests.
> 
> [   46.884442] *list_add double add*: new=ffff9b2ab7289330, prev=ffff9b2ab7289330, next=ffff9b2ab81e28e0.
> [   46.884476] Modules linked in: hci_uart btbcm bluetooth rfkill_gpio igb_avb(O) cfg80211 snd_soc_sst_bxt_tdf8532 snd_soc_skl snd_soc_skl_ipc snd_soc_sst_ipc snd_soc_sst_dsp snd_soc_sst_acpi snd_soc_sst_match snd_hda_ext_core snd_hda_core trusty_timer trusty_wall trusty_log trusty_virtio trusty_ipc trusty_mem trusty_irq trusty virtio_ring virtio intel_ipu4_mmu_bxtB0 lib2600_mod_bxtB0 intel_ipu4_isys_mod_bxtB0 lib2600psys_mod_bxtB0 intel_ipu4_psys_mod_bxtB0 intel_ipu4_mod_bxtB0 intel_ipu4_wrapper_bxtB0 intel_ipu4_acpi videobuf2_dma_contig as3638 dw9714 lm3643 crlmodule smiapp smiapp_pll
> [   46.884480] CPU: 1 PID: 33 Comm: kworker/u8:1 Tainted: G     U  W  O    4.9.56-quilt-2e5dc0ac-g618ed69ced6e-dirty #4
> [   46.884489] Workqueue: events_unbound flush_to_ldisc
> [   46.884494]  ffffb98ac012bb08 ffffffffad3e82e5 ffffb98ac012bb58 0000000000000000
> [   46.884497]  ffffb98ac012bb48 ffffffffad0a23d1 00000024ad6374dd ffff9b2ab7289330
> [   46.884500]  ffff9b2ab81e28e0 ffff9b2ab7289330 0000000000000002 0000000000000000
> [   46.884501] Call Trace:
> [   46.884507]  [<ffffffffad3e82e5>] dump_stack+0x67/0x92
> [   46.884511]  [<ffffffffad0a23d1>] __warn+0xd1/0xf0
> [   46.884513]  [<ffffffffad0a244f>] warn_slowpath_fmt+0x5f/0x80
> [   46.884516]  [<ffffffffad407443>] __list_add+0xb3/0xc0
> [   46.884521]  [<ffffffffad71133c>] *usb_anchor_urb*+0x4c/0xa0
> [   46.884524]  [<ffffffffad782c6f>] *acm_tty_flush_chars*+0x8f/0xb0
> [   46.884527]  [<ffffffffad782cd1>] *acm_tty_put_char*+0x41/0x100
> [   46.884530]  [<ffffffffad4ced34>] tty_put_char+0x24/0x40
> [   46.884533]  [<ffffffffad4d3bf5>] do_output_char+0xa5/0x200
> [   46.884535]  [<ffffffffad4d3e98>] __process_echoes+0x148/0x290
> [   46.884538]  [<ffffffffad4d654c>] n_tty_receive_buf_common+0x57c/0xb00
> [   46.884541]  [<ffffffffad4d6ae4>] n_tty_receive_buf2+0x14/0x20
> [   46.884543]  [<ffffffffad4d9662>] tty_ldisc_receive_buf+0x22/0x50
> [   46.884545]  [<ffffffffad4d9c05>] flush_to_ldisc+0xc5/0xe0
> [   46.884549]  [<ffffffffad0bcfe8>] process_one_work+0x148/0x440
> [   46.884551]  [<ffffffffad0bdc19>] worker_thread+0x69/0x4a0
> [   46.884554]  [<ffffffffad0bdbb0>] ? max_active_store+0x80/0x80
> [   46.884556]  [<ffffffffad0c2e10>] kthread+0x110/0x130
> [   46.884559]  [<ffffffffad0c2d00>] ? kthread_park+0x60/0x60
> [   46.884563]  [<ffffffffadad9917>] ret_from_fork+0x27/0x40
> [   46.884566] ---[ end trace 3bd599058b8a9eb3 ]---
> 
> Signed-off-by: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@xxxxxxxxx>

Why hasn't the author of this patch signed off on it?

thanks,

greg k-h