Re: [PATCH 7/7] libtrivfs: lock-less reference counting for trivfs_peropen objects

[Samuel Thibault]

Justus Winter, le Mon 26 May 2014 13:19:19 +0200, a écrit :
> * libtrivfs/trivfs.h (struct trivfs_peropen): Use refcount_t for field
> refcnt.
> (struct trivfs_control): Remove unused field lock.
> * libtrivfs/cntl-create.c (trivfs_create_control): Drop the mutex
> initialization.
> * libtrivfs/io-reauthenticate.c (trivfs_S_io_reauthenticate): Adjust
> accordingly.
> * libtrivfs/io-restrict-auth.c (trivfs_S_io_restrict_auth): Likewise.
> * libtrivfs/open.c (trivfs_open): Initialize refcnt.
> * libtrivfs/protid-clean.c (trivfs_clean_protid): Likewise.
> * libtrivfs/protid-dup.c (trivfs_protid_dup): Likewise.

Ack.

> ---
>  libtrivfs/cntl-create.c       |  1 -
>  libtrivfs/io-reauthenticate.c |  5 +----
>  libtrivfs/io-restrict-auth.c  |  4 +---
>  libtrivfs/open.c              |  2 +-
>  libtrivfs/protid-clean.c      | 29 ++++++++++++++++++-----------
>  libtrivfs/protid-dup.c        |  5 +----
>  libtrivfs/trivfs.h            |  4 ++--
>  7 files changed, 24 insertions(+), 26 deletions(-)
> 
> diff --git a/libtrivfs/cntl-create.c b/libtrivfs/cntl-create.c
> index 910daf3..eb9a834 100644
> --- a/libtrivfs/cntl-create.c
> +++ b/libtrivfs/cntl-create.c
> @@ -85,7 +85,6 @@ trivfs_create_control (mach_port_t underlying,
>       }
>  
>        (*control)->hook = 0;
> -      pthread_mutex_init (&(*control)->lock, NULL);
>      }
>  
>  out:
> diff --git a/libtrivfs/io-reauthenticate.c b/libtrivfs/io-reauthenticate.c
> index 7677697..df0ed2e 100644
> --- a/libtrivfs/io-reauthenticate.c
> +++ b/libtrivfs/io-reauthenticate.c
> @@ -62,11 +62,8 @@ trivfs_S_io_reauthenticate (struct trivfs_protid *cred,
>      newcred->isroot = 1;
>  
>    newcred->hook = cred->hook;
> -
> -  pthread_mutex_lock (&cred->po->cntl->lock);
>    newcred->po = cred->po;
> -  newcred->po->refcnt++;
> -  pthread_mutex_unlock (&cred->po->cntl->lock);
> +  refcount_ref (&newcred->po->refcnt);
>  
>    do
>      err = io_restrict_auth (newcred->po->cntl->underlying, 
> &newcred->realnode,
> diff --git a/libtrivfs/io-restrict-auth.c b/libtrivfs/io-restrict-auth.c
> index 65b4fd6..39670fe 100644
> --- a/libtrivfs/io-restrict-auth.c
> +++ b/libtrivfs/io-restrict-auth.c
> @@ -110,10 +110,8 @@ trivfs_S_io_restrict_auth (struct trivfs_protid *cred,
>      }
>  
>    newcred->isroot = 0;
> -  pthread_mutex_lock (&cred->po->cntl->lock);
>    newcred->po = cred->po;
> -  newcred->po->refcnt++;
> -  pthread_mutex_unlock (&cred->po->cntl->lock);
> +  refcount_ref (&newcred->po->refcnt);
>    if (cred->isroot && idvec_contains (user->uids, 0))
>      newcred->isroot = 1;
>    newcred->user = user;
> diff --git a/libtrivfs/open.c b/libtrivfs/open.c
> index f64d2ff..97e70a1 100644
> --- a/libtrivfs/open.c
> +++ b/libtrivfs/open.c
> @@ -40,7 +40,7 @@ trivfs_open (struct trivfs_control *cntl,
>  
>    ports_port_ref (cntl);
>  
> -  po->refcnt = 1;
> +  refcount_init (&po->refcnt, 1);
>    po->cntl = cntl;
>    po->openmodes = flags;
>    po->hook = 0;
> diff --git a/libtrivfs/protid-clean.c b/libtrivfs/protid-clean.c
> index f98da6a..86fbc19 100644
> --- a/libtrivfs/protid-clean.c
> +++ b/libtrivfs/protid-clean.c
> @@ -31,19 +31,26 @@ trivfs_clean_protid (void *arg)
>      (*trivfs_protid_destroy_hook) (cred);
>  
>    /* If we hold the only reference to the peropen, try to get rid of it. */
> -  pthread_mutex_lock (&cntl->lock);
> -  if (cred->po->refcnt == 1 && trivfs_peropen_destroy_hook)
> +  if (trivfs_peropen_destroy_hook)
>      {
> -      pthread_mutex_unlock (&cntl->lock);
> -      (*trivfs_peropen_destroy_hook) (cred->po);
> -      pthread_mutex_lock (&cntl->lock);
> +      if (refcount_deref (&cred->po->refcnt) == 0)
> +        {
> +          /* Reaquire a reference while we call the hook.  */
> +          refcount_ref (&cred->po->refcnt);
> +          (*trivfs_peropen_destroy_hook) (cred->po);
> +          if (refcount_deref (&cred->po->refcnt) == 0)
> +            {
> +              ports_port_deref (cntl);
> +              free (cred->po);
> +            }
> +        }
>      }
> -  if (--cred->po->refcnt == 0)
> -    {
> -      ports_port_deref (cntl);
> -      free (cred->po);
> -    }
> -  pthread_mutex_unlock (&cntl->lock);
> +  else
> +    if (refcount_deref (&cred->po->refcnt) == 0)
> +      {
> +        ports_port_deref (cntl);
> +        free (cred->po);
> +      }
>  
>    iohelp_free_iouser (cred->user);
>  
> diff --git a/libtrivfs/protid-dup.c b/libtrivfs/protid-dup.c
> index 6169603..75f3ca8 100644
> --- a/libtrivfs/protid-dup.c
> +++ b/libtrivfs/protid-dup.c
> @@ -35,11 +35,8 @@ trivfs_protid_dup (struct trivfs_protid *cred, struct 
> trivfs_protid **dup)
>  
>    if (! err)
>      {
> -      pthread_mutex_lock (&cred->po->cntl->lock);
>        new->po = cred->po;
> -      new->po->refcnt++;
> -      pthread_mutex_unlock (&cred->po->cntl->lock);
> -
> +      refcount_ref (&new->po->refcnt);
>        new->isroot = cred->isroot;
>  
>        err = iohelp_dup_iouser (&new->user, cred->user);
> diff --git a/libtrivfs/trivfs.h b/libtrivfs/trivfs.h
> index bb456ff..8902338 100644
> --- a/libtrivfs/trivfs.h
> +++ b/libtrivfs/trivfs.h
> @@ -24,6 +24,7 @@
>  #include <mach/mach.h>
>  #include <hurd/ports.h>
>  #include <hurd/iohelp.h>
> +#include <refcount.h>
>  
>  struct trivfs_protid
>  {
> @@ -41,14 +42,13 @@ struct trivfs_peropen
>  {
>    void *hook;                        /* for user use */
>    int openmodes;
> -  int refcnt;
> +  refcount_t refcnt;
>    struct trivfs_control *cntl;
>  };
>  
>  struct trivfs_control
>  {
>    struct port_info pi;
> -  pthread_mutex_t lock;
>    struct port_class *protid_class;
>    struct port_bucket *protid_bucket;
>    mach_port_t filesys_id;
> -- 
> 2.0.0.rc2
> 

-- 
Samuel
 RR> Ce que je cherche à démontrer, c'est qu'il est injuste de faire
 RR> l'amalgame entre du bulk mail et du courrier non-solicité très ciblé
 un suppositoire non reclamé, meme tres bien ciblé, reste un suppositoire.
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