linux-kernel - Re: [PATCH 08/19] staging: lustre: simplify waiting in ldlm_completion

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Message-ID: <alpine.LFD.2.21.1801171530410.11282@casper.infradead.org>
Date:   Wed, 17 Jan 2018 15:31:16 +0000 (GMT)
From:   James Simmons <jsimmons@...radead.org>
To:     NeilBrown <neilb@...e.com>
cc:     Oleg Drokin <oleg.drokin@...el.com>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        lustre <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 08/19] staging: lustre: simplify waiting in
 ldlm_completion_ast()


> If a signal-callback (lwi_on_signal) is set without lwi_allow_intr, as
> is the case in ldlm_completion_ast(), the behavior depends on the
> timeout set.
> 
> If a timeout is set, then signals are ignored.  If the timeout is
> reached, the timeout handler is called.  If the timeout handler
> return 0, which ldlm_expired_completion_wait() always does, the
> l_wait_event() switches to exactly the behavior if no timeout was set.
> 
> If no timeout is set, then "fatal" signals are not ignored.  If one
> arrives the callback is run, but as the callback is empty in this
> case, that is not relevant.
> 
> This can be simplified to:
>  if a timeout is wanted
>      wait_event_idle_timeout()
>      if that timed out, call the timeout handler
>  l_wait_event_abortable()
> 
> i.e. the code always waits indefinitely.  Sometimes it performs a
> non-abortable wait first.  Sometimes it doesn't.  But it only
> aborts before the condition is true if it is signaled.
> This doesn't quite agree with the comments and debug messages.


Reviewed-by: James Simmons <jsimmons@...radead.org>
 
> Signed-off-by: NeilBrown <neilb@...e.com>
> ---
>  drivers/staging/lustre/lustre/ldlm/ldlm_request.c |   55 +++++++--------------
>  1 file changed, 18 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/ldlm/ldlm_request.c b/drivers/staging/lustre/lustre/ldlm/ldlm_request.c
> index a244fa717134..f1233d844bbd 100644
> --- a/drivers/staging/lustre/lustre/ldlm/ldlm_request.c
> +++ b/drivers/staging/lustre/lustre/ldlm/ldlm_request.c
> @@ -72,15 +72,6 @@ MODULE_PARM_DESC(ldlm_enqueue_min, "lock enqueue timeout minimum");
>  /* in client side, whether the cached locks will be canceled before replay */
>  unsigned int ldlm_cancel_unused_locks_before_replay = 1;
>  
> -static void interrupted_completion_wait(void *data)
> -{
> -}
> -
> -struct lock_wait_data {
> -	struct ldlm_lock *lwd_lock;
> -	__u32	     lwd_conn_cnt;
> -};
> -
>  struct ldlm_async_args {
>  	struct lustre_handle lock_handle;
>  };
> @@ -112,10 +103,8 @@ static int ldlm_request_bufsize(int count, int type)
>  	return sizeof(struct ldlm_request) + avail;
>  }
>  
> -static int ldlm_expired_completion_wait(void *data)
> +static void ldlm_expired_completion_wait(struct ldlm_lock *lock, struct obd_import *imp2)
>  {
> -	struct lock_wait_data *lwd = data;
> -	struct ldlm_lock *lock = lwd->lwd_lock;
>  	struct obd_import *imp;
>  	struct obd_device *obd;
>  
> @@ -135,19 +124,17 @@ static int ldlm_expired_completion_wait(void *data)
>  			if (last_dump == 0)
>  				libcfs_debug_dumplog();
>  		}
> -		return 0;
> +		return;
>  	}
>  
>  	obd = lock->l_conn_export->exp_obd;
>  	imp = obd->u.cli.cl_import;
> -	ptlrpc_fail_import(imp, lwd->lwd_conn_cnt);
> +	ptlrpc_fail_import(imp, imp2 ? imp2->imp_conn_cnt : 0);
>  	LDLM_ERROR(lock,
>  		   "lock timed out (enqueued at %lld, %llds ago), entering recovery for %s@%s",
>  		   (s64)lock->l_last_activity,
>  		   (s64)(ktime_get_real_seconds() - lock->l_last_activity),
>  		   obd2cli_tgt(obd), imp->imp_connection->c_remote_uuid.uuid);
> -
> -	return 0;
>  }
>  
>  /**
> @@ -251,10 +238,8 @@ EXPORT_SYMBOL(ldlm_completion_ast_async);
>  int ldlm_completion_ast(struct ldlm_lock *lock, __u64 flags, void *data)
>  {
>  	/* XXX ALLOCATE - 160 bytes */
> -	struct lock_wait_data lwd;
>  	struct obd_device *obd;
>  	struct obd_import *imp = NULL;
> -	struct l_wait_info lwi;
>  	__u32 timeout;
>  	int rc = 0;
>  
> @@ -281,32 +266,28 @@ int ldlm_completion_ast(struct ldlm_lock *lock, __u64 flags, void *data)
>  
>  	timeout = ldlm_cp_timeout(lock);
>  
> -	lwd.lwd_lock = lock;
>  	lock->l_last_activity = ktime_get_real_seconds();
>  
> -	if (ldlm_is_no_timeout(lock)) {
> -		LDLM_DEBUG(lock, "waiting indefinitely because of NO_TIMEOUT");
> -		lwi = LWI_INTR(interrupted_completion_wait, &lwd);
> -	} else {
> -		lwi = LWI_TIMEOUT_INTR(timeout * HZ,
> -				       ldlm_expired_completion_wait,
> -				       interrupted_completion_wait, &lwd);
> -	}
> -
> -	if (imp) {
> -		spin_lock(&imp->imp_lock);
> -		lwd.lwd_conn_cnt = imp->imp_conn_cnt;
> -		spin_unlock(&imp->imp_lock);
> -	}
> -
>  	if (OBD_FAIL_CHECK_RESET(OBD_FAIL_LDLM_INTR_CP_AST,
>  				 OBD_FAIL_LDLM_CP_BL_RACE | OBD_FAIL_ONCE)) {
>  		ldlm_set_fail_loc(lock);
>  		rc = -EINTR;
>  	} else {
> -		/* Go to sleep until the lock is granted or cancelled. */
> -		rc = l_wait_event(lock->l_waitq,
> -				  is_granted_or_cancelled(lock), &lwi);
> +		/* Go to sleep until the lock is granted or canceled. */
> +		if (!ldlm_is_no_timeout(lock)) {
> +			/* Wait uninterruptible for a while first */
> +			rc = wait_event_idle_timeout(lock->l_waitq,
> +						     is_granted_or_cancelled(lock),
> +						     timeout * HZ);
> +			if (rc == 0)
> +				ldlm_expired_completion_wait(lock, imp);
> +		}
> +		/* Now wait abortable */
> +		if (rc == 0)
> +			rc = l_wait_event_abortable(lock->l_waitq,
> +						    is_granted_or_cancelled(lock));
> +		else
> +			rc = 0;
>  	}
>  
>  	if (rc) {
> 
> 
>