On Tue, Sep 17, 2019 at 01:31:05PM -0500, Mike Christie wrote:
> On 09/17/2019 06:56 AM, xiubli@xxxxxxxxxx wrote:
> > From: Xiubo Li <xiubli@xxxxxxxxxx>
> >
> > When the NBD_CFLAG_DESTROY_ON_DISCONNECT flag is set and at the same
> > time when the socket is closed due to the server daemon is restarted,
> > just before the last DISCONNET is totally done if we start a new connection
> > by using the old nbd_index, there will be crashing randomly, like:
> >
> > <3>[ 110.151949] block nbd1: Receive control failed (result -32)
> > <1>[ 110.152024] BUG: unable to handle page fault for address: 0000058000000840
> > <1>[ 110.152063] #PF: supervisor read access in kernel mode
> > <1>[ 110.152083] #PF: error_code(0x0000) - not-present page
> > <6>[ 110.152094] PGD 0 P4D 0
> > <4>[ 110.152106] Oops: 0000 [#1] SMP PTI
> > <4>[ 110.152120] CPU: 0 PID: 6698 Comm: kworker/u5:1 Kdump: loaded Not tainted 5.3.0-rc4+ #2
> > <4>[ 110.152136] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> > <4>[ 110.152166] Workqueue: knbd-recv recv_work [nbd]
> > <4>[ 110.152187] RIP: 0010:__dev_printk+0xd/0x67
> > <4>[ 110.152206] Code: 10 e8 c5 fd ff ff 48 8b 4c 24 18 65 48 33 0c 25 28 00 [...]
> > <4>[ 110.152244] RSP: 0018:ffffa41581f13d18 EFLAGS: 00010206
> > <4>[ 110.152256] RAX: ffffa41581f13d30 RBX: ffff96dd7374e900 RCX: 0000000000000000
> > <4>[ 110.152271] RDX: ffffa41581f13d20 RSI: 00000580000007f0 RDI: ffffffff970ec24f
> > <4>[ 110.152285] RBP: ffffa41581f13d80 R08: ffff96dd7fc17908 R09: 0000000000002e56
> > <4>[ 110.152299] R10: ffffffff970ec24f R11: 0000000000000003 R12: ffff96dd7374e900
> > <4>[ 110.152313] R13: 0000000000000000 R14: ffff96dd7374e9d8 R15: ffff96dd6e3b02c8
> > <4>[ 110.152329] FS: 0000000000000000(0000) GS:ffff96dd7fc00000(0000) knlGS:0000000000000000
> > <4>[ 110.152362] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > <4>[ 110.152383] CR2: 0000058000000840 CR3: 0000000067cc6002 CR4: 00000000001606f0
> > <4>[ 110.152401] Call Trace:
> > <4>[ 110.152422] _dev_err+0x6c/0x83
> > <4>[ 110.152435] nbd_read_stat.cold+0xda/0x578 [nbd]
> > <4>[ 110.152448] ? __switch_to_asm+0x34/0x70
> > <4>[ 110.152468] ? __switch_to_asm+0x40/0x70
> > <4>[ 110.152478] ? __switch_to_asm+0x34/0x70
> > <4>[ 110.152491] ? __switch_to_asm+0x40/0x70
> > <4>[ 110.152501] ? __switch_to_asm+0x34/0x70
> > <4>[ 110.152511] ? __switch_to_asm+0x40/0x70
> > <4>[ 110.152522] ? __switch_to_asm+0x34/0x70
> > <4>[ 110.152533] recv_work+0x35/0x9e [nbd]
> > <4>[ 110.152547] process_one_work+0x19d/0x340
> > <4>[ 110.152558] worker_thread+0x50/0x3b0
> > <4>[ 110.152568] kthread+0xfb/0x130
> > <4>[ 110.152577] ? process_one_work+0x340/0x340
> > <4>[ 110.152609] ? kthread_park+0x80/0x80
> > <4>[ 110.152637] ret_from_fork+0x35/0x40
> >
> > This is very easy to reproduce by running the nbd-runner.
> >
> > Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> > ---
> > drivers/block/nbd.c | 36 ++++++++++++++++++++++++++++++++++++
> > 1 file changed, 36 insertions(+)
> >
> > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > index 7e0501c47153..ac07e8c94c79 100644
> > --- a/drivers/block/nbd.c
> > +++ b/drivers/block/nbd.c
> > @@ -26,6 +26,7 @@
> > #include <linux/ioctl.h>
> > #include <linux/mutex.h>
> > #include <linux/compiler.h>
> > +#include <linux/completion.h>
> > #include <linux/err.h>
> > #include <linux/kernel.h>
> > #include <linux/slab.h>
> > @@ -80,6 +81,9 @@ struct link_dead_args {
> > #define NBD_RT_DESTROY_ON_DISCONNECT 6
> > #define NBD_RT_DISCONNECT_ON_CLOSE 7
> >
> > +#define NBD_DESTROY_ON_DISCONNECT 0
> > +#define NBD_DISCONNECT_REQUESTED 1
> > +
> > struct nbd_config {
> > u32 flags;
> > unsigned long runtime_flags;
> > @@ -113,6 +117,9 @@ struct nbd_device {
> > struct list_head list;
> > struct task_struct *task_recv;
> > struct task_struct *task_setup;
> > +
> > + struct completion *destroy_complete;
> > + unsigned long flags;
> > };
> >
> > #define NBD_CMD_REQUEUED 1
> > @@ -223,6 +230,16 @@ static void nbd_dev_remove(struct nbd_device *nbd)
> > disk->private_data = NULL;
> > put_disk(disk);
> > }
> > +
> > + /*
> > + * Place this in the last just before the nbd is freed to
> > + * make sure that the disk and the related kobject are also
> > + * totally removed to avoid duplicate creation of the same
> > + * one.
> > + */
> > + if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) && nbd->destroy_complete)
> > + complete(nbd->destroy_complete);
> > +
> > kfree(nbd);
> > }
> >
> > @@ -1125,6 +1142,7 @@ static int nbd_disconnect(struct nbd_device *nbd)
> >
> > dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
> > set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
> > + set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
> > send_disconnects(nbd);
> > return 0;
> > }
> > @@ -1636,6 +1654,7 @@ static int nbd_dev_add(int index)
> > nbd->tag_set.flags = BLK_MQ_F_SHOULD_MERGE |
> > BLK_MQ_F_BLOCKING;
> > nbd->tag_set.driver_data = nbd;
> > + nbd->destroy_complete = NULL;
> >
> > err = blk_mq_alloc_tag_set(&nbd->tag_set);
> > if (err)
> > @@ -1750,6 +1769,7 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
> >
> > static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
> > {
> > + DECLARE_COMPLETION_ONSTACK(destroy_complete);
> > struct nbd_device *nbd = NULL;
> > struct nbd_config *config;
> > int index = -1;
> > @@ -1801,6 +1821,17 @@ static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
> > mutex_unlock(&nbd_index_mutex);
> > return -EINVAL;
> > }
> > +
> > + if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
> > + test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) {
>
> You still need the nbd_put mutex part of the v3 patch don't you?
>
> nbd_dev_remove could call kfree(nbd) while we are accessing the nbd
> device struct above.
>
We're still holding the mutex here, so this is safe right?
> > + nbd->destroy_complete = &destroy_complete;
>
> Also, without the mutex part of the v3 patch, we could race and
> nbd_dev_remove could have passed the destroy_complete check already, so
> below we will wait forever.
>
Oh hmm you're right, we need to re-init the completion every time. I retract my
reviewed-by I guess. Thanks,
Josef
