9pfs: fix migration_block leak

[Qemu-devel] [PATCH] 9pfs: fix migration_block leak

Posted by Li Qiang 7 years ago

The guest can leave the pdu->s->migration_blocker exists by attach
but not remove a fid. Then if we hot unplug the 9pfs device, the
v9fs_reset() just free the fids, but not free the migration_blocker.
This will leak a memory leak. This patch avoid this.

Signed-off-by: Li Qiang <liqiang6-s@360.cn>
---
 hw/9pfs/9p.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 48babce..b55c02d 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
             free_fid(pdu, fidp);
         }
     }
+
+    if (pdu->s->migration_blocker) {
+        migrate_del_blocker(pdu->s->migration_blocker);
+        error_free(pdu->s->migration_blocker);
+        pdu->s->migration_blocker = NULL;
+    }
 }
 
 #define P9_QID_TYPE_DIR         0x80
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH for-2.9?] 9pfs: fix migration_block leak

Posted by Eric Blake 7 years ago

On 03/30/2017 07:27 AM, Li Qiang wrote:
> The guest can leave the pdu->s->migration_blocker exists by attach

s/exists/in place/
s/attach/attaching/

> but not remove a fid. Then if we hot unplug the 9pfs device, the

s/remove/removing/

> v9fs_reset() just free the fids, but not free the migration_blocker.
> This will leak a memory leak. This patch avoid this.

s/leak a/cause a/
s/avoid/avoids/

> 
> Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> ---
>  hw/9pfs/9p.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Probably worth including in 2.9 as a bug fix.

Reviewed-by: Eric Blake <eblake@redhat.com>

> 
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 48babce..b55c02d 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
>              free_fid(pdu, fidp);
>          }
>      }
> +
> +    if (pdu->s->migration_blocker) {
> +        migrate_del_blocker(pdu->s->migration_blocker);
> +        error_free(pdu->s->migration_blocker);
> +        pdu->s->migration_blocker = NULL;
> +    }
>  }
>  
>  #define P9_QID_TYPE_DIR         0x80
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Re: [Qemu-devel] [PATCH for-2.9?] 9pfs: fix migration_block leak

Posted by Greg Kurz 7 years ago

On Thu, 30 Mar 2017 08:25:25 -0500
Eric Blake <eblake@redhat.com> wrote:

> On 03/30/2017 07:27 AM, Li Qiang wrote:
> > The guest can leave the pdu->s->migration_blocker exists by attach  
> 
> s/exists/in place/
> s/attach/attaching/
> 
> > but not remove a fid. Then if we hot unplug the 9pfs device, the  
> 

In theory you're right, but the current 9p client in linux won't let you hot
unplug the device unless you unmount the 9p share first, hence freeing the
blocker.

> s/remove/removing/
> 
> > v9fs_reset() just free the fids, but not free the migration_blocker.
> > This will leak a memory leak. This patch avoid this.  

I had a similar issue sitting my TODO list for quite a time: the blocker
survives a system_reset. It doesn't cause a memory leak but it prevents
migration until the guest mounts/unmounts the 9p share again.

This boils down to virtfs_reset() calling free_fid() instead of put_fid() IIRC.

> 
> s/leak a/cause a/
> s/avoid/avoids/
> 
> > 
> > Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> > ---
> >  hw/9pfs/9p.c | 6 ++++++
> >  1 file changed, 6 insertions(+)  
> 
> Probably worth including in 2.9 as a bug fix.
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> > 
> > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > index 48babce..b55c02d 100644
> > --- a/hw/9pfs/9p.c
> > +++ b/hw/9pfs/9p.c
> > @@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
> >              free_fid(pdu, fidp);
> >          }
> >      }
> > +
> > +    if (pdu->s->migration_blocker) {
> > +        migrate_del_blocker(pdu->s->migration_blocker);
> > +        error_free(pdu->s->migration_blocker);
> > +        pdu->s->migration_blocker = NULL;
> > +    }

I'd prefer to drain all PDUs in virtfs_reset() and have the loop above
to call put_fid() instead of free_fid(). If this isn't doable for 2.9,
I'll apply this patch with a comment.

> >  }
> >  
> >  #define P9_QID_TYPE_DIR         0x80
> >   
>

Re: [Qemu-devel] [PATCH for-2.9?] 9pfs: fix migration_block leak

Posted by Li Qiang 7 years ago

Hello,

2017-03-30 23:46 GMT+08:00 Greg Kurz <groug@kaod.org>:

> On Thu, 30 Mar 2017 08:25:25 -0500
> Eric Blake <eblake@redhat.com> wrote:
>
> > On 03/30/2017 07:27 AM, Li Qiang wrote:
> > > The guest can leave the pdu->s->migration_blocker exists by attach
> >
> > s/exists/in place/
> > s/attach/attaching/
> >
>

Eric,
Thanks for pointing my mistakes!


> > > but not remove a fid. Then if we hot unplug the 9pfs device, the
> >
>
> In theory you're right, but the current 9p client in linux won't let you
> hot
> unplug the device unless you unmount the 9p share first, hence freeing the
> blocker.
>
>
I think we should consider every possible situation.


> > s/remove/removing/
> >
> > > v9fs_reset() just free the fids, but not free the migration_blocker.
> > > This will leak a memory leak. This patch avoid this.
>
> I had a similar issue sitting my TODO list for quite a time: the blocker
> survives a system_reset. It doesn't cause a memory leak but it prevents
> migration until the guest mounts/unmounts the 9p share again.
>
> This boils down to virtfs_reset() calling free_fid() instead of put_fid()
> IIRC.
>
> >
> > s/leak a/cause a/
> > s/avoid/avoids/
> >
> > >
> > > Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> > > ---
> > >  hw/9pfs/9p.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> >
> > Probably worth including in 2.9 as a bug fix.
> >
> > Reviewed-by: Eric Blake <eblake@redhat.com>
> >
> > >
> > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > > index 48babce..b55c02d 100644
> > > --- a/hw/9pfs/9p.c
> > > +++ b/hw/9pfs/9p.c
> > > @@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU
> *pdu)
> > >              free_fid(pdu, fidp);
> > >          }
> > >      }
> > > +
> > > +    if (pdu->s->migration_blocker) {
> > > +        migrate_del_blocker(pdu->s->migration_blocker);
> > > +        error_free(pdu->s->migration_blocker);
> > > +        pdu->s->migration_blocker = NULL;
> > > +    }
>
> I'd prefer to drain all PDUs in virtfs_reset() and have the loop above
> to call put_fid() instead of free_fid(). If this isn't doable for 2.9,
> I'll apply this patch with a comment.
>
>
Yes, I have considered to use put_fid() to fix this. But I'm not sure the
'fidp->ref' is  at most 1 in virtfs_reset() function(I think it is).

IIUC I think omit the 'else' branch, and call put_fid() directly like this.

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 48babce..ae97e79 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -544,9 +544,8 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)

         if (fidp->ref) {
             fidp->clunked = 1;
-        } else {
-            free_fid(pdu, fidp);
         }
+        put_fid(pdu, fidp);
     }
 }


If you agree, I will send a formal patch.



> > >  }
> > >
> > >  #define P9_QID_TYPE_DIR         0x80
> > >
> >
>
>

Re: [Qemu-devel] [PATCH for-2.9?] 9pfs: fix migration_block leak

Posted by Greg Kurz 7 years ago

On Fri, 31 Mar 2017 09:26:35 +0800
Li Qiang <liq3ea@gmail.com> wrote:

> Hello,
> 
> 2017-03-30 23:46 GMT+08:00 Greg Kurz <groug@kaod.org>:
> 
> > On Thu, 30 Mar 2017 08:25:25 -0500
> > Eric Blake <eblake@redhat.com> wrote:
> >
> > > On 03/30/2017 07:27 AM, Li Qiang wrote:
> > > > The guest can leave the pdu->s->migration_blocker exists by attach
> > >
> > > s/exists/in place/
> > > s/attach/attaching/
> > >
> >
> 
> Eric,
> Thanks for pointing my mistakes!
> 
> 
> > > > but not remove a fid. Then if we hot unplug the 9pfs device, the
> > >
> >
> > In theory you're right, but the current 9p client in linux won't let you
> > hot
> > unplug the device unless you unmount the 9p share first, hence freeing the
> > blocker.
> >
> >
> I think we should consider every possible situation.
> 
> 
> > > s/remove/removing/
> > >
> > > > v9fs_reset() just free the fids, but not free the migration_blocker.
> > > > This will leak a memory leak. This patch avoid this.
> >
> > I had a similar issue sitting my TODO list for quite a time: the blocker
> > survives a system_reset. It doesn't cause a memory leak but it prevents
> > migration until the guest mounts/unmounts the 9p share again.
> >
> > This boils down to virtfs_reset() calling free_fid() instead of put_fid()
> > IIRC.
> >
> > >
> > > s/leak a/cause a/
> > > s/avoid/avoids/
> > >
> > > >
> > > > Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> > > > ---
> > > >  hw/9pfs/9p.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > >
> > > Probably worth including in 2.9 as a bug fix.
> > >
> > > Reviewed-by: Eric Blake <eblake@redhat.com>
> > >
> > > >
> > > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > > > index 48babce..b55c02d 100644
> > > > --- a/hw/9pfs/9p.c
> > > > +++ b/hw/9pfs/9p.c
> > > > @@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU
> > *pdu)
> > > >              free_fid(pdu, fidp);
> > > >          }
> > > >      }
> > > > +
> > > > +    if (pdu->s->migration_blocker) {
> > > > +        migrate_del_blocker(pdu->s->migration_blocker);
> > > > +        error_free(pdu->s->migration_blocker);
> > > > +        pdu->s->migration_blocker = NULL;
> > > > +    }
> >
> > I'd prefer to drain all PDUs in virtfs_reset() and have the loop above
> > to call put_fid() instead of free_fid(). If this isn't doable for 2.9,
> > I'll apply this patch with a comment.
> >
> >
> Yes, I have considered to use put_fid() to fix this. But I'm not sure the
> 'fidp->ref' is  at most 1 in virtfs_reset() function(I think it is).
> 

And indeed, if the fid is involved in an I/O then its ref will be != 0.

> IIUC I think omit the 'else' branch, and call put_fid() directly like this.
> 

This won't work: we must ensure that fidp->ref reaches zero (ie, drain
all PDUs), then we can fidp->ref++ (ie, get a ref on the fid) and call
put_fid(), which will drop the last ref of the fid and clear the blocker
if this is the root fid.

> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index 48babce..ae97e79 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -544,9 +544,8 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
> 
>          if (fidp->ref) {
>              fidp->clunked = 1;
> -        } else {
> -            free_fid(pdu, fidp);
>          }
> +        put_fid(pdu, fidp);
>      }
>  }
> 
> 
> If you agree, I will send a formal patch.
> 
> 
> 
> > > >  }
> > > >
> > > >  #define P9_QID_TYPE_DIR         0x80
> > > >
> > >
> >
> >

Re: [Qemu-devel] [PATCH for-2.9?] 9pfs: fix migration_block leak

Posted by Li Qiang 7 years ago

2017-03-31 15:07 GMT+08:00 Greg Kurz <groug@kaod.org>:

> On Fri, 31 Mar 2017 09:26:35 +0800
> Li Qiang <liq3ea@gmail.com> wrote:
>
> > Hello,
> >
> > 2017-03-30 23:46 GMT+08:00 Greg Kurz <groug@kaod.org>:
> >
> > > On Thu, 30 Mar 2017 08:25:25 -0500
> > > Eric Blake <eblake@redhat.com> wrote:
> > >
> > > > On 03/30/2017 07:27 AM, Li Qiang wrote:
> > > > > The guest can leave the pdu->s->migration_blocker exists by attach
> > > >
> > > > s/exists/in place/
> > > > s/attach/attaching/
> > > >
> > >
> >
> > Eric,
> > Thanks for pointing my mistakes!
> >
> >
> > > > > but not remove a fid. Then if we hot unplug the 9pfs device, the
> > > >
> > >
> > > In theory you're right, but the current 9p client in linux won't let
> you
> > > hot
> > > unplug the device unless you unmount the 9p share first, hence freeing
> the
> > > blocker.
> > >
> > >
> > I think we should consider every possible situation.
> >
> >
> > > > s/remove/removing/
> > > >
> > > > > v9fs_reset() just free the fids, but not free the
> migration_blocker.
> > > > > This will leak a memory leak. This patch avoid this.
> > >
> > > I had a similar issue sitting my TODO list for quite a time: the
> blocker
> > > survives a system_reset. It doesn't cause a memory leak but it prevents
> > > migration until the guest mounts/unmounts the 9p share again.
> > >
> > > This boils down to virtfs_reset() calling free_fid() instead of
> put_fid()
> > > IIRC.
> > >
> > > >
> > > > s/leak a/cause a/
> > > > s/avoid/avoids/
> > > >
> > > > >
> > > > > Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> > > > > ---
> > > > >  hw/9pfs/9p.c | 6 ++++++
> > > > >  1 file changed, 6 insertions(+)
> > > >
> > > > Probably worth including in 2.9 as a bug fix.
> > > >
> > > > Reviewed-by: Eric Blake <eblake@redhat.com>
> > > >
> > > > >
> > > > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > > > > index 48babce..b55c02d 100644
> > > > > --- a/hw/9pfs/9p.c
> > > > > +++ b/hw/9pfs/9p.c
> > > > > @@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU
> > > *pdu)
> > > > >              free_fid(pdu, fidp);
> > > > >          }
> > > > >      }
> > > > > +
> > > > > +    if (pdu->s->migration_blocker) {
> > > > > +        migrate_del_blocker(pdu->s->migration_blocker);
> > > > > +        error_free(pdu->s->migration_blocker);
> > > > > +        pdu->s->migration_blocker = NULL;
> > > > > +    }
> > >
> > > I'd prefer to drain all PDUs in virtfs_reset() and have the loop above
> > > to call put_fid() instead of free_fid(). If this isn't doable for 2.9,
> > > I'll apply this patch with a comment.
> > >
> > >
> > Yes, I have considered to use put_fid() to fix this. But I'm not sure the
> > 'fidp->ref' is  at most 1 in virtfs_reset() function(I think it is).
> >
>
> And indeed, if the fid is involved in an I/O then its ref will be != 0.
>
> > IIUC I think omit the 'else' branch, and call put_fid() directly like
> this.
> >
>
> This won't work: we must ensure that fidp->ref reaches zero (ie, drain
> all PDUs), then we can fidp->ref++ (ie, get a ref on the fid) and call
> put_fid(), which will drop the last ref of the fid and clear the blocker
> if this is the root fid.
>
>
Right, but how can we ensure we have drained all PDUs? Any idea?

Thanks.



> > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > index 48babce..ae97e79 100644
> > --- a/hw/9pfs/9p.c
> > +++ b/hw/9pfs/9p.c
> > @@ -544,9 +544,8 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
> >
> >          if (fidp->ref) {
> >              fidp->clunked = 1;
> > -        } else {
> > -            free_fid(pdu, fidp);
> >          }
> > +        put_fid(pdu, fidp);
> >      }
> >  }
> >
> >
> > If you agree, I will send a formal patch.
> >
> >
> >
> > > > >  }
> > > > >
> > > > >  #define P9_QID_TYPE_DIR         0x80
> > > > >
> > > >
> > >
> > >
>
>

Re: [Qemu-devel] [PATCH for-2.9?] 9pfs: fix migration_block leak

Posted by Greg Kurz 7 years ago

On Fri, 31 Mar 2017 16:01:15 +0800
Li Qiang <liq3ea@gmail.com> wrote:

> 2017-03-31 15:07 GMT+08:00 Greg Kurz <groug@kaod.org>:
> 
> > On Fri, 31 Mar 2017 09:26:35 +0800
> > Li Qiang <liq3ea@gmail.com> wrote:
> >
> > > Hello,
> > >
> > > 2017-03-30 23:46 GMT+08:00 Greg Kurz <groug@kaod.org>:
> > >
> > > > On Thu, 30 Mar 2017 08:25:25 -0500
> > > > Eric Blake <eblake@redhat.com> wrote:
> > > >
> > > > > On 03/30/2017 07:27 AM, Li Qiang wrote:
> > > > > > The guest can leave the pdu->s->migration_blocker exists by attach
> > > > >
> > > > > s/exists/in place/
> > > > > s/attach/attaching/
> > > > >
> > > >
> > >
> > > Eric,
> > > Thanks for pointing my mistakes!
> > >
> > >
> > > > > > but not remove a fid. Then if we hot unplug the 9pfs device, the
> > > > >
> > > >
> > > > In theory you're right, but the current 9p client in linux won't let
> > you
> > > > hot
> > > > unplug the device unless you unmount the 9p share first, hence freeing
> > the
> > > > blocker.
> > > >
> > > >
> > > I think we should consider every possible situation.
> > >
> > >
> > > > > s/remove/removing/
> > > > >
> > > > > > v9fs_reset() just free the fids, but not free the
> > migration_blocker.
> > > > > > This will leak a memory leak. This patch avoid this.
> > > >
> > > > I had a similar issue sitting my TODO list for quite a time: the
> > blocker
> > > > survives a system_reset. It doesn't cause a memory leak but it prevents
> > > > migration until the guest mounts/unmounts the 9p share again.
> > > >
> > > > This boils down to virtfs_reset() calling free_fid() instead of
> > put_fid()
> > > > IIRC.
> > > >
> > > > >
> > > > > s/leak a/cause a/
> > > > > s/avoid/avoids/
> > > > >
> > > > > >
> > > > > > Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> > > > > > ---
> > > > > >  hw/9pfs/9p.c | 6 ++++++
> > > > > >  1 file changed, 6 insertions(+)
> > > > >
> > > > > Probably worth including in 2.9 as a bug fix.
> > > > >
> > > > > Reviewed-by: Eric Blake <eblake@redhat.com>
> > > > >
> > > > > >
> > > > > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > > > > > index 48babce..b55c02d 100644
> > > > > > --- a/hw/9pfs/9p.c
> > > > > > +++ b/hw/9pfs/9p.c
> > > > > > @@ -548,6 +548,12 @@ static void coroutine_fn virtfs_reset(V9fsPDU
> > > > *pdu)
> > > > > >              free_fid(pdu, fidp);
> > > > > >          }
> > > > > >      }
> > > > > > +
> > > > > > +    if (pdu->s->migration_blocker) {
> > > > > > +        migrate_del_blocker(pdu->s->migration_blocker);
> > > > > > +        error_free(pdu->s->migration_blocker);
> > > > > > +        pdu->s->migration_blocker = NULL;
> > > > > > +    }
> > > >
> > > > I'd prefer to drain all PDUs in virtfs_reset() and have the loop above
> > > > to call put_fid() instead of free_fid(). If this isn't doable for 2.9,
> > > > I'll apply this patch with a comment.
> > > >
> > > >
> > > Yes, I have considered to use put_fid() to fix this. But I'm not sure the
> > > 'fidp->ref' is  at most 1 in virtfs_reset() function(I think it is).
> > >
> >
> > And indeed, if the fid is involved in an I/O then its ref will be != 0.
> >
> > > IIUC I think omit the 'else' branch, and call put_fid() directly like
> > this.
> > >
> >
> > This won't work: we must ensure that fidp->ref reaches zero (ie, drain
> > all PDUs), then we can fidp->ref++ (ie, get a ref on the fid) and call
> > put_fid(), which will drop the last ref of the fid and clear the blocker
> > if this is the root fid.
> >
> >
> Right, but how can we ensure we have drained all PDUs? Any idea?
> 

Yep, I'll send patches shorty and Cc you.

> Thanks.
> 
> 
> 
> > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > > index 48babce..ae97e79 100644
> > > --- a/hw/9pfs/9p.c
> > > +++ b/hw/9pfs/9p.c
> > > @@ -544,9 +544,8 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
> > >
> > >          if (fidp->ref) {
> > >              fidp->clunked = 1;
> > > -        } else {
> > > -            free_fid(pdu, fidp);
> > >          }
> > > +        put_fid(pdu, fidp);
> > >      }
> > >  }
> > >
> > >
> > > If you agree, I will send a formal patch.
> > >
> > >
> > >
> > > > > >  }
> > > > > >
> > > > > >  #define P9_QID_TYPE_DIR         0x80
> > > > > >
> > > > >
> > > >
> > > >
> >
> >