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Message-ID: <d5c47d35-91b1-0d57-34bf-b848aa15c562@redhat.com>
Date:   Thu, 28 Jul 2022 09:16:36 -0400
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Subject: Re: [PATCH] Eliminate deadlocks in connects with an MT environment
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To:     Attila Kovacs <attila.kovacs@cfa.harvard.edu>,
        Libtirpc-devel Mailing List 
        <libtirpc-devel@lists.sourceforge.net>
Cc:     Linux NFS Mailing list <linux-nfs@vger.kernel.org>
References: <20220720212057.43986-1-attila.kovacs@cfa.harvard.edu>
From:   Steve Dickson <steved@redhat.com>
In-Reply-To: <20220720212057.43986-1-attila.kovacs@cfa.harvard.edu>
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On 7/20/22 5:20 PM, Attila Kovacs wrote:
> In cnlt_dg_freeres() and clnt_vc_freeres(), cond_signal() is called after
> unlocking the mutex (clnt_fd_lock). The manual of pthread_cond_signal()
> allows that, but mentions that for consistent scheduling, cond_signal()
> should be called with the waiting mutex locked.
> 
> clnt_fd_lock is locked on L171, but then not released if jumping to the
> err1 label on an error (L175 and L180). This means that those errors
> will deadlock all further operations that require clnt_fd_lock access.
> 
> Same in clnt_vc.c in clnt_vc_create, on lines 215, 222, and 230 respectively.
> 
> Signed-off-by: Steve Dickson <steved@redhat.com>
Committed (tag: libtirpc-1-3-3-rc4)

steved.

> ---
> [Reposting Attila's patch with the proper Signed-off-by and format]
> 
>   src/clnt_dg.c |  9 ++++++---
>   src/clnt_vc.c | 12 ++++++++----
>   2 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/src/clnt_dg.c b/src/clnt_dg.c
> index b3d82e7..7c5d22e 100644
> --- a/src/clnt_dg.c
> +++ b/src/clnt_dg.c
> @@ -101,9 +101,9 @@ extern mutex_t clnt_fd_lock;
>   #define	release_fd_lock(fd_lock, mask) {	\
>   	mutex_lock(&clnt_fd_lock);	\
>   	fd_lock->active = FALSE;	\
> -	mutex_unlock(&clnt_fd_lock);	\
>   	thr_sigsetmask(SIG_SETMASK, &(mask), NULL); \
>   	cond_signal(&fd_lock->cv);	\
> +	mutex_unlock(&clnt_fd_lock);    \
>   }
>   
>   static const char mem_err_clnt_dg[] = "clnt_dg_create: out of memory";
> @@ -172,12 +172,15 @@ clnt_dg_create(fd, svcaddr, program, version, sendsz, recvsz)
>   	if (dg_fd_locks == (fd_locks_t *) NULL) {
>   		dg_fd_locks = fd_locks_init();
>   		if (dg_fd_locks == (fd_locks_t *) NULL) {
> +			mutex_unlock(&clnt_fd_lock);
>   			goto err1;
>   		}
>   	}
>   	fd_lock = fd_lock_create(fd, dg_fd_locks);
> -	if (fd_lock == (fd_lock_t *) NULL)
> +	if (fd_lock == (fd_lock_t *) NULL) {
> +		mutex_unlock(&clnt_fd_lock);
>   		goto err1;
> +	}
>   
>   	mutex_unlock(&clnt_fd_lock);
>   	thr_sigsetmask(SIG_SETMASK, &(mask), NULL);
> @@ -573,9 +576,9 @@ clnt_dg_freeres(cl, xdr_res, res_ptr)
>   	cu->cu_fd_lock->active = TRUE;
>   	xdrs->x_op = XDR_FREE;
>   	dummy = (*xdr_res)(xdrs, res_ptr);
> -	mutex_unlock(&clnt_fd_lock);
>   	thr_sigsetmask(SIG_SETMASK, &mask, NULL);
>   	cond_signal(&cu->cu_fd_lock->cv);
> +	mutex_unlock(&clnt_fd_lock);
>   	return (dummy);
>   }
>   
> diff --git a/src/clnt_vc.c b/src/clnt_vc.c
> index a07e297..3c73e65 100644
> --- a/src/clnt_vc.c
> +++ b/src/clnt_vc.c
> @@ -153,9 +153,9 @@ extern mutex_t  clnt_fd_lock;
>   #define release_fd_lock(fd_lock, mask) {	\
>   	mutex_lock(&clnt_fd_lock);	\
>   	fd_lock->active = FALSE;	\
> -	mutex_unlock(&clnt_fd_lock);	\
>   	thr_sigsetmask(SIG_SETMASK, &(mask), (sigset_t *) NULL);	\
>   	cond_signal(&fd_lock->cv);	\
> +	mutex_unlock(&clnt_fd_lock);    \
>   }
>   
>   static const char clnt_vc_errstr[] = "%s : %s";
> @@ -216,7 +216,9 @@ clnt_vc_create(fd, raddr, prog, vers, sendsz, recvsz)
>   	if (vc_fd_locks == (fd_locks_t *) NULL) {
>   		vc_fd_locks = fd_locks_init();
>   		if (vc_fd_locks == (fd_locks_t *) NULL) {
> -			struct rpc_createerr *ce = &get_rpc_createerr();
> +			struct rpc_createerr *ce;
> +			mutex_unlock(&clnt_fd_lock);
> +			ce = &get_rpc_createerr();
>   			ce->cf_stat = RPC_SYSTEMERROR;
>   			ce->cf_error.re_errno = errno;
>   			goto err;
> @@ -224,7 +226,9 @@ clnt_vc_create(fd, raddr, prog, vers, sendsz, recvsz)
>   	}
>   	fd_lock = fd_lock_create(fd, vc_fd_locks);
>   	if (fd_lock == (fd_lock_t *) NULL) {
> -		struct rpc_createerr *ce = &get_rpc_createerr();
> +		struct rpc_createerr *ce;
> +		mutex_unlock(&clnt_fd_lock);
> +		ce = &get_rpc_createerr();
>   		ce->cf_stat = RPC_SYSTEMERROR;
>   		ce->cf_error.re_errno = errno;
>   		goto err;
> @@ -495,9 +499,9 @@ clnt_vc_freeres(cl, xdr_res, res_ptr)
>   		cond_wait(&ct->ct_fd_lock->cv, &clnt_fd_lock);
>   	xdrs->x_op = XDR_FREE;
>   	dummy = (*xdr_res)(xdrs, res_ptr);
> -	mutex_unlock(&clnt_fd_lock);
>   	thr_sigsetmask(SIG_SETMASK, &(mask), NULL);
>   	cond_signal(&ct->ct_fd_lock->cv);
> +	mutex_unlock(&clnt_fd_lock);
>   
>   	return dummy;
>   }