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[174.3.196.123]) by smtp.gmail.com with ESMTPSA id t68-v6sm14554420pfe.91.2018.06.22.14.13.46 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Jun 2018 14:13:47 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.86_2) (envelope-from ) id 1fWTNK-00024z-16; Fri, 22 Jun 2018 15:13:46 -0600 Date: Fri, 22 Jun 2018 15:13:46 -0600 From: Jason Gunthorpe To: Stefan Berger Cc: linux-integrity@vger.kernel.org, jarkko.sakkinen@linux.intel.com, zohar@linux.vnet.ibm.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/4] tpm: Implement tpm_chip_find() for other subsystems to find a TPM chip Message-ID: <20180622211346.GF19151@ziepe.ca> References: <20180622164613.1609313-1-stefanb@linux.vnet.ibm.com> <20180622164613.1609313-3-stefanb@linux.vnet.ibm.com> <20180622204319.GE19151@ziepe.ca> <6f4d9302-8399-e73a-f8d0-d493658c1980@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f4d9302-8399-e73a-f8d0-d493658c1980@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 04:45:47PM -0400, Stefan Berger wrote: > On 06/22/2018 04:43 PM, Jason Gunthorpe wrote: > >On Fri, Jun 22, 2018 at 12:46:11PM -0400, Stefan Berger wrote: > >>Implement tpm_chip_find() for other subsystems to find a TPM chip and > >>get a reference to that chip. > >> > >>Signed-off-by: Stefan Berger > >> drivers/char/tpm/tpm-chip.c | 27 +++++++++++++++++++++++++++ > >> include/linux/tpm.h | 5 +++++ > >> 2 files changed, 32 insertions(+) > >> > >>diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c > >>index 4e83695af068..2520555b1e17 100644 > >>+++ b/drivers/char/tpm/tpm-chip.c > >>@@ -81,6 +81,33 @@ void tpm_put_ops(struct tpm_chip *chip) > >> EXPORT_SYMBOL_GPL(tpm_put_ops); > >> /** > >>+ * tpm_chip_find() - find a TPM chip and get a reference to it > >>+ */ > >>+struct tpm_chip *tpm_chip_find(void) > >I feel like this should be called 'tpm_default_chip()' > > > >>+{ > >>+ struct tpm_chip *chip, *res = NULL; > >>+ int chip_num = 0; > >>+ int chip_prev; > >>+ > >>+ mutex_lock(&idr_lock); > >>+ > >>+ do { > >>+ chip_prev = chip_num; > >>+ chip = idr_get_next(&dev_nums_idr, &chip_num); > >>+ if (chip) { > >>+ get_device(&chip->dev); > >>+ res = chip; > >>+ break; > >>+ } > >>+ } while (chip_prev != chip_num); > >>+ > >>+ mutex_unlock(&idr_lock); > >And what was tpm_chip_find_get should just call this function.. > And then after that each time tpm_get_ops() ? It is best to keep the tpm_chip_find_get/tpm_put_ops for internal use as it also manages the kref lifetime of chip in a subtle way, it relies on the ops lock not the kref to keep the memory valid when it has a NULL parameter.. Something like this: struct tpm_chip *tpm_find_get_ops(struct tpm_chip *chip) { int rc; if (chip) { if (!tpm_try_get_ops(chip)) return NULL; return chip; } chip = tpm_default_chip(); rc = tpm_try_get_ops(chip)); put_device(&chip->dev); if (rc) return NULL; return chip; } Jason