On Mon, Sep 29, 2025 at 04:16:02PM +0800, Jinhui Guo wrote:
> The command "ipmi -b -t" would occasionally fail:
> #ipmitool -b 6 -t 0x2c raw 0x6 0x01
> Unable to send command: Invalid argument
> Unable to send RAW command (channel=0x6 netfn=0x6 lun=0x0 cmd=0x1)
>
> The race window between __scan_channels() and deliver_response() causes
> the parameters of some channels to be set to 0.
>
> 1.[CPUA] After ipmi_add_smi() calling __bmc_get_device_id() ->
> __scan_channels(), the intf->channels_ready is set to true and
> is never cleared by any function. ipmi_add_smi() then invokes
> __scan_channels(), which issues an IPMI request and waits with
> wait_event() until all channels have been scanned. wait_event()
> internally calls might_sleep(), which might yield the CPU.
> (wait_event() could also be interrupted by an interrupt, causing
> the task to yield the CPU.)
> 2.[CPUB] deliver_response() is invoked when the CPU receives the IPMI
> response. After processing a IPMI response, deliver_response()
> directly assigns intf->wchannels to intf->channel_list and sets
> intf->channels_ready to true. However, not all channels are actually
> ready for use.
> 3.[CPUA] Since intf->channels_ready is already true, wait_event() never
> enters __wait_event(). __scan_channels() immediately clears
> intf->null_user_handler and exits.
> 4.[CPUB] Once intf->null_user_handler is set to NULL, deliver_response()
> ignores further IPMI responses, leaving the remaining channels
> zero-initialized and unusable.
>
> CPUA CPUB
> ------------------------------- -----------------------------
> ipmi_add_smi()
> __scan_channels()
> intf->null_user_handler
> = channel_handler;
> send_channel_info_cmd(intf,
> 0);
> wait_event(intf->waitq,
> intf->channels_ready);
> do {
> might_sleep();
> deliver_response()
> channel_handler()
> intf->channel_list =
> intf->wchannels + set;
> intf->channels_ready = true;
> send_channel_info_cmd(intf,
> intf->curr_channel);
> if (condition)
> break;
> __wait_event(wq_head,
> condition);
> } while(0)
> intf->null_user_handler
> = NULL;
> deliver_response()
> if (!msg->user)
> if (intf->null_user_handler)
> rv = -EINVAL;
> return rv;
> ------------------------------- -----------------------------
>
> Fix the race between __scan_channels() and deliver_response() with the
> following changes.
>
> 1. Drop the redundant __scan_channels() call in ipmi_add_smi(), the
> function is already invoked via ipmi_add_smi() -> __bmc_get_device_id()
> -> __scan_channels().
It's only called conditionally in __bmc_get_device_id(), what if it's
not called there?
> 2. channel_handler() sets intf->channels_ready to true but no one clears
> it, preventing __scan_channels() from rescanning channels. Clear
> intf->channels_ready to false in channel_handler() before starting
> the channel scan.
This is mostly the intent. The channels shouldn't change unless the BMC
software changes.
The only exception would be after the comment:
/* Version info changes, scan the channels again. */
__scan_channels(intf, &bmc->fetch_id);
In that case, since the BMC has changed, you want to rescan the channels.
So you would want to reset that flag there.
> 3. Only assign intf->channel_list = intf->wchannels and set
> intf->channels_ready = true in channel_handler() after all channels
> have been successfully scanned or after failing to send the IPMI
> request.
Yeah, that's a bug.
Normal style is to leave the {} in if any part of the if statement has
braces.
Also, the above three are independent problems; they should be separate
patches.
Thanks,
-corey
>
> Signed-off-by: Jinhui Guo <[email protected]>
> ---
> drivers/char/ipmi/ipmi_msghandler.c | 14 ++++----------
> 1 file changed, 4 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c
> b/drivers/char/ipmi/ipmi_msghandler.c
> index 8e9050f99e9e..73dab3b21221 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -3405,11 +3405,8 @@ channel_handler(struct ipmi_smi *intf, struct
> ipmi_recv_msg *msg)
> intf->channel_list = intf->wchannels + set;
> intf->channels_ready = true;
> wake_up(&intf->waitq);
> - } else {
> - intf->channel_list = intf->wchannels + set;
> - intf->channels_ready = true;
> + } else
> rv = send_channel_info_cmd(intf, intf->curr_channel);
> - }
>
> if (rv) {
> /* Got an error somehow, just give up. */
> @@ -3433,6 +3430,9 @@ static int __scan_channels(struct ipmi_smi *intf,
> struct ipmi_device_id *id)
> {
> int rv;
>
> + /* Clear channels_ready to force channels rescan. */
> + intf->channels_ready = false;
> +
> if (ipmi_version_major(id) > 1
> || (ipmi_version_major(id) == 1
> && ipmi_version_minor(id) >= 5)) {
> @@ -3633,12 +3633,6 @@ int ipmi_add_smi(struct module *owner,
> goto out_err_started;
> }
>
> - mutex_lock(&intf->bmc_reg_mutex);
> - rv = __scan_channels(intf, &id);
> - mutex_unlock(&intf->bmc_reg_mutex);
> - if (rv)
> - goto out_err_bmc_reg;
> -
> intf->nr_users_devattr = dev_attr_nr_users;
> sysfs_attr_init(&intf->nr_users_devattr.attr);
> rv = device_create_file(intf->si_dev, &intf->nr_users_devattr);
> --
> 2.20.1
>
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