linux-kernel - Re: [PATCH] tpm: Revert "tpm: fix invalid locking in NONBLOCKING mode"

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Date:   Tue, 26 May 2020 12:39:37 -0700
From:   Tadeusz Struk <tstruk@...il.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Mario Limonciello <mario.limonciello@...l.com>,
        Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jeffrin Jose T <jeffrin@...agiritech.edu.in>,
        Alex Guzman <alex@...man.io>
Subject: Re: [PATCH] tpm: Revert "tpm: fix invalid locking in NONBLOCKING
 mode"

On 5/26/20 12:14 PM, James Bottomley wrote:
> +	/* atomic tpm command send and result receive. We only hold the ops
> +	 * lock during this period so that the tpm can be unregistered even if
> +	 * the char dev is held open.
> +	 */
> +	if (tpm_try_get_ops(priv->chip)) {
> +		ret = -EPIPE;
> +		goto out;
> +	}
> +
Hi James,
This won't help if the message is read by an async tcti. If the problem lies
in the chip get locality code, perhaps this could help to debug the root-cause
instead of masking it out in the upper layer code:

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 2435216bd10a..da5ecd0376bf 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -202,20 +202,22 @@ static int request_locality(struct tpm_chip *chip, int l)
 		return rc;
 
 	stop = jiffies + chip->timeout_a;
+	timeout = stop - jiffies;
 
 	if (chip->flags & TPM_CHIP_FLAG_IRQ) {
 again:
 		timeout = stop - jiffies;
 		if ((long)timeout <= 0)
-			return -1;
+			goto out;
+
 		rc = wait_event_interruptible_timeout(priv->int_queue,
-						      (check_locality
-						       (chip, l)),
+						      check_locality(chip, l),
 						      timeout);
 		if (rc > 0)
 			return l;
 		if (rc == -ERESTARTSYS && freezing(current)) {
 			clear_thread_flag(TIF_SIGPENDING);
+			timeout = stop - jiffies;
 			goto again;
 		}
 	} else {
@@ -226,6 +228,10 @@ static int request_locality(struct tpm_chip *chip, int l)
 			tpm_msleep(TPM_TIMEOUT);
 		} while (time_before(jiffies, stop));
 	}
+out:
+	dev_warn(&chip->dev, "%s: failed to request locality %d after %lu ms\n",
+			 __func__, l, timeout * HZ / 1000);
+
 	return -1;
 }