There is a rare race when we remove an entry from the global list hv_context.percpu_list[cpu] in hv_process_channel_removal() -> percpu_channel_deq() -> list_del(): at this time, if vmbus_on_event() -> process_chn_event() -> pcpu_relid2channel() is trying to query the list, we can get the kernel fault. Similarly, we also have the issue in the code path: vmbus_process_offer() -> percpu_channel_enq(). We can resolve the issue by disabling the tasklet when updating the list. The patch also moves vmbus_release_relid() to a later place where the channel has been removed from the per-cpu and the global lists. Reported-by: Rolf Neugebauer <rolf.neugebauer@xxxxxxxxxx> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> --- v2: added tasklet_schedule() after tasklet_enable(). Thanks, Vitaly! v3: I shouldn't have moved percpu_channel_deq() from hv_process_channel_removal() to vmbus_close_internal(): the channel couldn't be removed from the per-cpu list, if the channel state was not CHANNEL_OPENED_STATE. v3 fixed this. v3 also added 2 wrapper functions for the disable/enable stuff. v3 also moved vmbus_release_relid() to a later safe place. v4: fixed a copy-and-paste bug in vmbus_process_offer(): "hv_event_tasklet_disable(channel) and hv_event_tasklet_enable(channel)" are buggy: the 'channel' parameter should be 'newchannel'. Thanks Vitaly for this! You can also get the patch on https://github.com/dcui/linux/commits/decui/hv_sock/net-next/20160601_v11 drivers/hv/channel.c | 6 ++---- drivers/hv/channel_mgmt.c | 32 ++++++++++++++++++++++++++++---- include/linux/hyperv.h | 3 +++ 3 files changed, 33 insertions(+), 8 deletions(-) diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c index 56dd261..ef8e9b5 100644 --- a/drivers/hv/channel.c +++ b/drivers/hv/channel.c @@ -512,7 +512,6 @@ static void reset_channel_cb(void *arg) static int vmbus_close_internal(struct vmbus_channel *channel) { struct vmbus_channel_close_channel *msg; - struct tasklet_struct *tasklet; int ret; /* @@ -524,8 +523,7 @@ static int vmbus_close_internal(struct vmbus_channel *channel) * To resolve the race, we can serialize them by disabling the * tasklet when the latter is running here. */ - tasklet = hv_context.event_dpc[channel->target_cpu]; - tasklet_disable(tasklet); + hv_event_tasklet_disable(channel); /* * In case a device driver's probe() fails (e.g., @@ -591,7 +589,7 @@ static int vmbus_close_internal(struct vmbus_channel *channel) get_order(channel->ringbuffer_pagecount * PAGE_SIZE)); out: - tasklet_enable(tasklet); + hv_event_tasklet_enable(channel); return ret; } diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c index 38b682ba..fd89c4c 100644 --- a/drivers/hv/channel_mgmt.c +++ b/drivers/hv/channel_mgmt.c @@ -21,6 +21,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include <linux/kernel.h> +#include <linux/interrupt.h> #include <linux/sched.h> #include <linux/wait.h> #include <linux/mm.h> @@ -303,16 +304,32 @@ static void vmbus_release_relid(u32 relid) vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released)); } +void hv_event_tasklet_disable(struct vmbus_channel *channel) +{ + struct tasklet_struct *tasklet; + tasklet = hv_context.event_dpc[channel->target_cpu]; + tasklet_disable(tasklet); +} + +void hv_event_tasklet_enable(struct vmbus_channel *channel) +{ + struct tasklet_struct *tasklet; + tasklet = hv_context.event_dpc[channel->target_cpu]; + tasklet_enable(tasklet); + + /* In case there is any pending event */ + tasklet_schedule(tasklet); +} + void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid) { unsigned long flags; struct vmbus_channel *primary_channel; - vmbus_release_relid(relid); - BUG_ON(!channel->rescind); BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex)); + hv_event_tasklet_disable(channel); if (channel->target_cpu != get_cpu()) { put_cpu(); smp_call_function_single(channel->target_cpu, @@ -321,6 +338,7 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid) percpu_channel_deq(channel); put_cpu(); } + hv_event_tasklet_enable(channel); if (channel->primary_channel == NULL) { list_del(&channel->listentry); @@ -341,6 +359,8 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid) cpumask_clear_cpu(channel->target_cpu, &primary_channel->alloced_cpus_in_node); + vmbus_release_relid(relid); + free_channel(channel); } @@ -409,6 +429,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) init_vp_index(newchannel, dev_type); + hv_event_tasklet_disable(newchannel); if (newchannel->target_cpu != get_cpu()) { put_cpu(); smp_call_function_single(newchannel->target_cpu, @@ -418,6 +439,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) percpu_channel_enq(newchannel); put_cpu(); } + hv_event_tasklet_enable(newchannel); /* * This state is used to indicate a successful open @@ -463,12 +485,11 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) return; err_deq_chan: - vmbus_release_relid(newchannel->offermsg.child_relid); - mutex_lock(&vmbus_connection.channel_mutex); list_del(&newchannel->listentry); mutex_unlock(&vmbus_connection.channel_mutex); + hv_event_tasklet_disable(newchannel); if (newchannel->target_cpu != get_cpu()) { put_cpu(); smp_call_function_single(newchannel->target_cpu, @@ -477,6 +498,9 @@ err_deq_chan: percpu_channel_deq(newchannel); put_cpu(); } + hv_event_tasklet_enable(newchannel); + + vmbus_release_relid(newchannel->offermsg.child_relid); err_free_chan: free_channel(newchannel); diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 7be7237..8070cda 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -1328,6 +1328,9 @@ extern bool vmbus_prep_negotiate_resp(struct icmsg_hdr *, struct icmsg_negotiate *, u8 *, int, int); +void hv_event_tasklet_disable(struct vmbus_channel *channel); +void hv_event_tasklet_enable(struct vmbus_channel *channel); + void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid); /* -- 2.1.0 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
