On Mon, Mar 7, 2016 at 4:44 PM, Yishai Hadas <yishaih@xxxxxxxxxxxxxxxxxx> wrote:
> On 3/7/2016 11:44 AM, Devesh Sharma wrote:
>>
>> Fixes: 35d4a0b63dc0 ("IB/uverbs: Fix race between ib_uverbs_open and
>> remove_one")
>
>
> It fixes 036b10635739 (IB/uverbs: Enable device removal when there are
> active user space applications) and not the commit that you pointed on.
>
>
>
>>
>> While testing ocrdma for disassociate_ucontext support following
>> kernel panic was seen:
>>
>> BUG: unable to handle kernel paging request at ffffffffa07ccd7a
>> [67139.981020] IP: [<ffffffffa07ccd7a>] 0xffffffffa07ccd7a
>> [67139.987185] PGD 19c5067 PUD 19c6063 PMD 469d08067 PTE 0
>> [67139.993370] Oops: 0010 [#1] SMP
>> [67140.257286] Call Trace:
>> [67140.260665] [<ffffffff810c16a0>] ? prepare_to_wait_event+0xf0/0xf0
>> [67140.268337] [<ffffffffa04cabc3>] ? ib_dereg_mr+0x23/0x30 [ib_core]
>> [67140.276009] [<ffffffffa03ee5f0>] ?
>> ib_uverbs_cleanup_ucontext+0x320/0x440 [ib_uverbs]
>> [67140.285550] [<ffffffffa03ee9e9>] ? ib_uverbs_close+0x59/0xb0
>> [ib_uverbs]
>> [67140.293807] [<ffffffff811ff744>] ? __fput+0xe4/0x210
>> [67140.300132] [<ffffffff811ff8ae>] ? ____fput+0xe/0x10
>> [67140.306457] [<ffffffff8109b697>] ? task_work_run+0x77/0x90
>> [67140.313388] [<ffffffff81081af2>] ? do_exit+0x2d2/0xab0
>> [67140.319910] [<ffffffff8108234f>] ? do_group_exit+0x3f/0xa0
>> [67140.326821] [<ffffffff8108d54c>] ? get_signal+0x1cc/0x5e0
>> [67140.333635] [<ffffffff81017387>] ? do_signal+0x37/0x660
>> [67140.340257] [<ffffffffa021669a>] ? ucma_write+0x7a/0xc0 [rdma_ucm]
>> [67140.347949] [<ffffffff81079c37>] ? exit_to_usermode_loop+0x59/0xa2
>> [67140.355651] [<ffffffff81003bad>] ? syscall_return_slowpath+0x8d/0xa0
>> [67140.363554] [<ffffffff81680dcc>] ? int_ret_from_sys_call+0x25/0x8f
>> [67140.371259] Code: Bad RIP value.
>> [67140.375678] RIP [<ffffffffa07ccd7a>] 0xffffffffa07ccd7a
>> [67140.382314] RSP <ffff880867727ad8>
>> [67140.386894] CR2: ffffffffa07ccd7a
>> [67140.393737] ---[ end trace 807b4472c30412d0 ]---
>> [67141.682413] Kernel panic - not syncing: Fatal exception
>> [67141.682431] Kernel Offset: disabled
>> [67141.733934] ---[ end Kernel panic - not syncing: Fatal exception
>>
>> Root Cause:
>>
>> During rmmod <vendor-driver> "ib_uverbs_close()" context is
>> still running, while "ib_uverbs_remove_one()" context completes and
>> ends up freeing ib_dev pointer, thus causing a Kernel Panic.
>
>
> Kernel Panic -> kernel panic.
Will fix this in V3.
>>
>>
>> This patch fixes the race. ib_uverbs_close validates dev->ib_dev against
>> NULL
>> inside an srcu lock. If it is NULL, it waits for a completion and drops
>> the srcu
>> else continues with the normal flow.
>
>
> Need to fix this description as of the expected code change, see below.
> Please also describe why/how it solves the problem and not what it does.
Sure, will do that.
>
>
>>
>> CC: Yishai Hadas <yishaih@xxxxxxxxxxxx>
>> Signed-off-by: Devesh Sharma <devesh.sharma@xxxxxxxxxxxx>
>> ---
>> drivers/infiniband/core/uverbs.h | 1 +
>> drivers/infiniband/core/uverbs_main.c | 18 ++++++++++++++++--
>> 2 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/infiniband/core/uverbs.h
>> b/drivers/infiniband/core/uverbs.h
>> index 612ccfd..94a7339 100644
>> --- a/drivers/infiniband/core/uverbs.h
>> +++ b/drivers/infiniband/core/uverbs.h
>> @@ -121,6 +121,7 @@ struct ib_uverbs_file {
>> struct ib_event_handler event_handler;
>> struct ib_uverbs_event_file *async_file;
>> struct list_head list;
>> + struct completion fcomp;
>> int is_closed;
>> };
>>
>> diff --git a/drivers/infiniband/core/uverbs_main.c
>> b/drivers/infiniband/core/uverbs_main.c
>> index 39680ae..9531168 100644
>> --- a/drivers/infiniband/core/uverbs_main.c
>> +++ b/drivers/infiniband/core/uverbs_main.c
>> @@ -928,6 +928,7 @@ static int ib_uverbs_open(struct inode *inode, struct
>> file *filp)
>> file->async_file = NULL;
>> kref_init(&file->ref);
>> mutex_init(&file->mutex);
>> + init_completion(&file->fcomp);
>>
>> filp->private_data = file;
>> kobject_get(&dev->kobj);
>> @@ -954,21 +955,33 @@ static int ib_uverbs_close(struct inode *inode,
>> struct file *filp)
>> struct ib_uverbs_file *file = filp->private_data;
>> struct ib_uverbs_device *dev = file->device;
>> struct ib_ucontext *ucontext = NULL;
>> + struct ib_device *ib_dev;
>> + int srcu_key;
>>
>> - mutex_lock(&file->device->lists_mutex);
>> + srcu_key = srcu_read_lock(&dev->disassociate_srcu);
>> + ib_dev = srcu_dereference(dev->ib_dev,
>> + &dev->disassociate_srcu);
>> + if (!ib_dev)
>
>
> You need to free the sruc lock, wait for completion then go to out.
> Doing in the opposite order as you did below, might end up with a dead-lock
> in case ib_uverbs_free_hw_resources is waiting for the
> synchronize_srcu(disassociate_srcu) and can't mark the file as completed.
Agreed. Will fix it.
>
>> + goto out;
>> +
>> + mutex_lock(&dev->lists_mutex);
>> ucontext = file->ucontext;
>> file->ucontext = NULL;
>> if (!file->is_closed) {
>> list_del(&file->list);
>> file->is_closed = 1;
>> }
>> - mutex_unlock(&file->device->lists_mutex);
>> + mutex_unlock(&dev->lists_mutex);
>> if (ucontext)
>> ib_uverbs_cleanup_ucontext(file, ucontext);
>>
>> if (file->async_file)
>> kref_put(&file->async_file->ref,
>> ib_uverbs_release_event_file);
>>
>> + complete(&file->fcomp);
>
>
> No need to do that in that flow, only in above flow.
Agreed.
>
>> +out:
>> + wait_for_completion(&file->fcomp);
>> + srcu_read_unlock(&dev->disassociate_srcu, srcu_key);
>
>
> See above, might end-up with a dead-lock, should be done above in opposite
> order.
Will fix in next version.
>
>
>> kref_put(&file->ref, ib_uverbs_release_file);
>> kobject_put(&dev->kobj);
>>
>> @@ -1199,6 +1212,7 @@ static void ib_uverbs_free_hw_resources(struct
>> ib_uverbs_device *uverbs_dev,
>> }
>>
>> mutex_lock(&uverbs_dev->lists_mutex);
>> + complete(&file->fcomp);
>> kref_put(&file->ref, ib_uverbs_release_file);
>> }
>>
>>
>
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