linux-kernel - Re: [PATCH v2] checkpatch: check for nested unlikely calls

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Message-ID: <9655ddea-a98d-073c-f130-e9345517f44f@linux.com>
Date:   Wed, 28 Aug 2019 18:36:53 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] checkpatch: check for nested unlikely calls

On 8/28/19 4:32 PM, Denis Efremov wrote:
> IS_ERR, IS_ERR_OR_NULL, IS_ERR_VALUE already contain unlikely optimization
> internally. Thus, there is no point in calling these functions under
> likely/unlikely.

It looks like this rule could be extended with this list:
CHECK_DATA_CORRUPTION
GLOCK_BUG_ON
SPIN_BUG_ON
RWLOCK_BUG_ON
DCCP_BUG_ON
GEM_BUG_ON
BUG_ON
WARN
WARN_TAINT
WARN_ON_ONCE
WARN_ONCE
WARN_TAINT_ONCE
WARN_ON_SMP

However, grep shows that maybe only BUG_ON, WARN_ON, WARN, WARN_ON_ONCE worth checking:
git grep 'likely(\s*\(CHECK_DATA_CORRUPTION\|GLOCK_BUG_ON\|SPIN_BUG_ON\|RWLOCK_BUG_ON\|DCCP_BUG_ON\|GEM_BUG_ON\|BUG_ON\|WARN\|WARN_TAINT\|WARN_ON_ONCE\|WARN_ONCE\|WARN_TAINT_ONCE\|WARN_ON_SMP\)' .
drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c:       if (unlikely(WARN_ON(!mixer))) {
drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c:       if (unlikely(WARN_ON(ctl_cfg->count > MAX_CTL))) {
drivers/gpu/drm/msm/disp/mdp_format.c:  if (unlikely(WARN_ON(type >= CSC_MAX)))
drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c:     if (unlikely(WARN_ON_ONCE(tls_ctx->netdev != netdev)))
drivers/net/wimax/i2400m/tx.c:          if (unlikely(WARN_ON(pad_buf == NULL
drivers/xen/events/events_base.c:       if (unlikely(WARN(irq >= nr_irqs, "Invalid irq %d!\n", irq)))
fs/open.c:      if (unlikely(WARN_ON(!f->f_op))) {
fs/xfs/xfs_buf.c:       if (unlikely(WARN_ON(!bp->b_ops || !bp->b_ops->magic[idx])))
fs/xfs/xfs_buf.c:       if (unlikely(WARN_ON(!bp->b_ops || !bp->b_ops->magic16[idx])))

> +# nested likely/unlikely calls
		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*((?:IS_ERR(?:_OR_NULL|_VALUE)?)|(?:BUG_ON|WARN(?:_ON(?:_ONCE)?)?)))/) {
or maybe even to match all possible WARNs:
		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*((?:IS_ERR(?:_OR_NULL|_VALUE)?)|(?:BUG_ON|WARN)))/) {
> +			WARN("LIKELY_MISUSE",
> +			     "nested (un)?likely calls, unlikely already used in $1 internally\n" . $herecurr);
> +		}

Any suggestions for v3?

Thanks,
Denis