-stable according to the previous conversation. > From: Rafael J. Wysocki [mailto:rjw@xxxxxxx] > Sent: Thursday, July 25, 2013 7:38 AM > > On Tuesday, July 23, 2013 04:09:15 PM Lv Zheng wrote: > > This patch fixes races caused by unprotected ACPI IPMI transfers. > > > > We can see the following crashes may occur: > > 1. There is no tx_msg_lock held for iterating tx_msg_list in > > ipmi_flush_tx_msg() while it is parellel unlinked on failure in > > acpi_ipmi_space_handler() under protection of tx_msg_lock. > > 2. There is no lock held for freeing tx_msg in acpi_ipmi_space_handler() > > while it is parellel accessed in ipmi_flush_tx_msg() and > > ipmi_msg_handler(). > > > > This patch enhances tx_msg_lock to protect all tx_msg accesses to > > solve this issue. Then tx_msg_lock is always held around complete() > > and tx_msg accesses. > > Calling smp_wmb() before setting msg_done flag so that messages > > completed due to flushing will not be handled as 'done' messages while > > their contents are not vaild. > > > > Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx> > > Cc: Zhao Yakui <yakui.zhao@xxxxxxxxx> > > Reviewed-by: Huang Ying <ying.huang@xxxxxxxxx> > > --- > > drivers/acpi/acpi_ipmi.c | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/acpi/acpi_ipmi.c b/drivers/acpi/acpi_ipmi.c index > > b37c189..527ee43 100644 > > --- a/drivers/acpi/acpi_ipmi.c > > +++ b/drivers/acpi/acpi_ipmi.c > > @@ -230,11 +230,14 @@ static void ipmi_flush_tx_msg(struct > acpi_ipmi_device *ipmi) > > struct acpi_ipmi_msg *tx_msg, *temp; > > int count = HZ / 10; > > struct pnp_dev *pnp_dev = ipmi->pnp_dev; > > + unsigned long flags; > > > > + spin_lock_irqsave(&ipmi->tx_msg_lock, flags); > > list_for_each_entry_safe(tx_msg, temp, &ipmi->tx_msg_list, head) { > > /* wake up the sleep thread on the Tx msg */ > > complete(&tx_msg->tx_complete); > > } > > + spin_unlock_irqrestore(&ipmi->tx_msg_lock, flags); > > > > /* wait for about 100ms to flush the tx message list */ > > while (count--) { > > @@ -268,13 +271,12 @@ static void ipmi_msg_handler(struct > ipmi_recv_msg *msg, void *user_msg_data) > > break; > > } > > } > > - spin_unlock_irqrestore(&ipmi_device->tx_msg_lock, flags); > > > > if (!msg_found) { > > dev_warn(&pnp_dev->dev, > > "Unexpected response (msg id %ld) is returned.\n", > > msg->msgid); > > - goto out_msg; > > + goto out_lock; > > } > > > > /* copy the response data to Rx_data buffer */ @@ -286,10 +288,14 @@ > > static void ipmi_msg_handler(struct ipmi_recv_msg *msg, void > *user_msg_data) > > } > > tx_msg->rx_len = msg->msg.data_len; > > memcpy(tx_msg->data, msg->msg.data, tx_msg->rx_len); > > + /* tx_msg content must be valid before setting msg_done flag */ > > + smp_wmb(); > > That's suspicious. > > If you need the write barrier here, you'll most likely need a read barrier > somewhere else. Where's that? It might depend on whether the content written before the smp_wmb() is used or not by the other side codes under the condition set after the smp_wmb(). So comment could be treated as 2 parts: 1. do we need a paired smp_rmb(). 2. do we need a smp_wmb(). For 1. If we want a paired smp_rmb(), then it will appear in this function: 186 static void acpi_format_ipmi_response(struct acpi_ipmi_msg *msg, 187 acpi_integer *value, int rem_time) 188 { 189 struct acpi_ipmi_buffer *buffer; 190 191 /* 192 * value is also used as output parameter. It represents the response 193 * IPMI message returned by IPMI command. 194 */ 195 buffer = (struct acpi_ipmi_buffer *)value; 196 if (!rem_time && !msg->msg_done) { 197 buffer->status = ACPI_IPMI_TIMEOUT; 198 return; 199 } 200 /* 201 * If the flag of msg_done is not set or the recv length is zero, it 202 * means that the IPMI command is not executed correctly. 203 * The status code will be ACPI_IPMI_UNKNOWN. 204 */ 205 if (!msg->msg_done || !msg->rx_len) { 206 buffer->status = ACPI_IPMI_UNKNOWN; 207 return; 208 } + smp_rmb(); 209 /* 210 * If the IPMI response message is obtained correctly, the status code 211 * will be ACPI_IPMI_OK 212 */ 213 buffer->status = ACPI_IPMI_OK; 214 buffer->length = msg->rx_len; 215 memcpy(buffer->data, msg->rx_data, msg->rx_len); 216 } If we don't then there will only be msg content not correctly read from msg->rx_data. Note that the rx_len is 0 during initialization and will never exceed the sizeof(buffer->data), so the read is safe. Being without smp_rmb() is also OK in this case, since: 1. buffer->data will never be used when buffer->status is not ACPI_IPMI_OK and 2. the smp_rmb()/smp_wmb() added in this patch will be deleted in [PATCH 07]. So IMO, we needn't add the smp_rmb(), what do you think of this? For 2. If we don't add smp_wmb() in the ipmi_msg_handler(), then the codes running on other thread in the acpi_format_ipmi_response() may read wrong msg->rx_data (a timeout triggers this function, but when acpi_format_ipmi_response() is entered, the msg->msg_done flag could be seen as 1 but the msg->rx_data is not ready), this is what we want to avoid in this quick fix. Thanks and best regards -Lv > > > tx_msg->msg_done = 1; > > > > out_comp: > > complete(&tx_msg->tx_complete); > > +out_lock: > > + spin_unlock_irqrestore(&ipmi_device->tx_msg_lock, flags); > > out_msg: > > ipmi_free_recv_msg(msg); > > } > > Rafael > > > -- > I speak only for myself. > Rafael J. 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