From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yishai Hadas Subject: Re: [PATCH V2] IB/uverbs: Fix race between uverbs_close and remove_one Date: Mon, 7 Mar 2016 13:14:29 +0200 Message-ID: <56DD6295.6000705@dev.mellanox.co.il> References: <1457343873-14869-1-git-send-email-devesh.sharma@broadcom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1457343873-14869-1-git-send-email-devesh.sharma-dY08KVG/lbpWk0Htik3J/w@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Devesh Sharma , dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, yishaih-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, Majd Dibbiny List-Id: linux-rdma@vger.kernel.org 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: [] 0xffffffffa07ccd7a > [67139.987185] PGD 19c5067 PUD 19c6063 PMD 469d08067 PTE 0 > [67139.993370] Oops: 0010 [#1] SMP > [67140.257286] Call Trace: > [67140.260665] [] ? prepare_to_wait_event+0xf0/0xf0 > [67140.268337] [] ? ib_dereg_mr+0x23/0x30 [ib_core] > [67140.276009] [] ? ib_uverbs_cleanup_ucontext+0x320/0x440 [ib_uverbs] > [67140.285550] [] ? ib_uverbs_close+0x59/0xb0 [ib_uverbs] > [67140.293807] [] ? __fput+0xe4/0x210 > [67140.300132] [] ? ____fput+0xe/0x10 > [67140.306457] [] ? task_work_run+0x77/0x90 > [67140.313388] [] ? do_exit+0x2d2/0xab0 > [67140.319910] [] ? do_group_exit+0x3f/0xa0 > [67140.326821] [] ? get_signal+0x1cc/0x5e0 > [67140.333635] [] ? do_signal+0x37/0x660 > [67140.340257] [] ? ucma_write+0x7a/0xc0 [rdma_ucm] > [67140.347949] [] ? exit_to_usermode_loop+0x59/0xa2 > [67140.355651] [] ? syscall_return_slowpath+0x8d/0xa0 > [67140.363554] [] ? int_ret_from_sys_call+0x25/0x8f > [67140.371259] Code: Bad RIP value. > [67140.375678] RIP [] 0xffffffffa07ccd7a > [67140.382314] RSP > [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 "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. > > 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. > > CC: Yishai Hadas > Signed-off-by: Devesh Sharma > --- > 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. > + 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. > +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. > 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); > } > > -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html