From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DBD9228DCA for ; Mon, 18 Mar 2024 09:01:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710752475; cv=none; b=Q7RWJYczDyfrakL0TjJGbxc4iEsxSqefQcFUvoi2vGGP9Xu3PV17JJd2UMz5Nm+q2q77GxgrUyjtURdhephoDSgxWRx0rXyyYAhuwlvF1uL+74/Givxx/v0GXOo4Yw3qfDlyxqKrEfWnbEbMyWT1q9aoRx6A9S2Y+oZqMcWOx7I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710752475; c=relaxed/simple; bh=2o4/pJGqG1gzwjf7h/MbArnmzBbXAOBen6beh+yYECQ=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=jgTZuHNyWF/aupvX+6+gMNspvo+MMW0RwGVe/Z+DPszUHDgNNxrUhLTm3FgHLjlO7EEza4sIFfpCJGQFWqGciDv1M1G9JNrVhPomaRq5EekyHCaR+Cn20AcbfnBjOS2tae1ibsM2hbfG8gP3vDCjqdmkxi3/fwiDJHZo+/eqjh0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Bk5ws+Zg; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=BN4mcNZW; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Bk5ws+Zg"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="BN4mcNZW" Date: Mon, 18 Mar 2024 10:01:08 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1710752469; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=r8EiV2gzXftggen6GL4Tj807WdurcECVI7Wmk1Mm55w=; b=Bk5ws+ZgAtsMmV/Bg61xGm2mYCJmRY1ttMRepbifFjRw2oBPFnjigwB9BMyTt1v13+r6GR i4eVBe6dZDPGIGv7sVGTx5zwrxqwKAoKKOzmUEnz3+AUG+5EntntcD52cgkuqb6yxg6pVD JWRo3UZvmSoao/JhGhxziakluoCDkKobdNXf546RjEzTRBij65hL4KzUTlPc43gohDiGEF 4sfmHgdsNV9yNq2UA6ID0c1jDk6AKprxiA7Pg2hElMPTw5ZEaPkMTWPPn58hipDXUmqEun 2whEubn+xf0z1U1NbIK5W2nM5K1jTwQFk/gu3/RbAsT15gVzyYv7av2DN+sE+Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1710752469; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=r8EiV2gzXftggen6GL4Tj807WdurcECVI7Wmk1Mm55w=; b=BN4mcNZW9LJt+7aw5DLrhZ/IG4G7TFzgzFAyO7MnMOJYNUH5J4LApJkR/eC35IYIKmeomT GZcT9f5k6/I/x6BA== From: Nam Cao To: Eva Kurchatova Cc: linux-riscv , bugs@lists.linux.dev, linux-i2c@vger.kernel.org, jikos@kernel.org, benjamin.tissoires@redhat.com, dianders@chromium.org, mripard@kernel.org, johan+linaro@kernel.org, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Boot hang with SiFive PLIC when routing I2C-HID level-triggered interrupts Message-ID: <20240318100108.4fafd72b@namcao> In-Reply-To: References: <20240317222718.3e03edb1@namcao> Precedence: bulk X-Mailing-List: bugs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 18/Mar/2024 Eva Kurchatova wrote: > On Sun, Mar 17, 2024 at 11:27=E2=80=AFPM Nam Cao w= rote: > > It seems I2C HID's interrupt handler (i2c_hid_irq) returns immediately = if > > I2C_HID_READ_PENDING is set. This flag is supposed to be cleared in > > i2c_hid_xfer(), but since the (threaded) interrupt handler runs at high= er > > priority, the flag is never cleared. So we have a lock-up: interrupt > > handler won't do anything unless the flag is cleared, but the clearing = of > > this flag is done in a lower priority task which never gets scheduled w= hile > > the interrupt handler is active. > > > > There is RT throttling to prevent RT tasks from locking up the system l= ike > > this. I don't know much about scheduling stuffs, so I am not really sure > > why RT throttling does not work. I think because RT throttling triggers > > when RT tasks take too much CPU time, but in this case hard interrupt > > handlers take lots of CPU time too (~50% according to my measurement), = so > > RT throttling doesn't trigger often enough (in this case, it triggers o= nce > > and never again). Again, I don't know much about scheduler so I may be > > talking nonsense here. > > > > The flag I2C_HID_READ_PENDING seems to be used to make sure that only 1 > > I2C operation can happen at a time. But this seems pointless, because I= 2C > > subsystem already takes care of this. So I think we can just remove it. > > > > Can you give the below patch a try? > > > > diff --git a/drivers/hid/i2c-hid/i2c-hid-core.c b/drivers/hid/i2c-hid/i= 2c-hid-core.c > > index 2735cd585af0..799ad0ef9c4a 100644 > > --- a/drivers/hid/i2c-hid/i2c-hid-core.c > > +++ b/drivers/hid/i2c-hid/i2c-hid-core.c > > @@ -64,7 +64,6 @@ > > /* flags */ > > #define I2C_HID_STARTED 0 > > #define I2C_HID_RESET_PENDING 1 > > -#define I2C_HID_READ_PENDING 2 > > > > #define I2C_HID_PWR_ON 0x00 > > #define I2C_HID_PWR_SLEEP 0x01 > > @@ -190,15 +189,10 @@ static int i2c_hid_xfer(struct i2c_hid *ihid, > > msgs[n].len =3D recv_len; > > msgs[n].buf =3D recv_buf; > > n++; > > - > > - set_bit(I2C_HID_READ_PENDING, &ihid->flags); > > } > > > > ret =3D i2c_transfer(client->adapter, msgs, n); > > > > - if (recv_len) > > - clear_bit(I2C_HID_READ_PENDING, &ihid->flags); > > - > > if (ret !=3D n) > > return ret < 0 ? ret : -EIO; > > > > @@ -566,9 +560,6 @@ static irqreturn_t i2c_hid_irq(int irq, void *dev_i= d) > > { > > struct i2c_hid *ihid =3D dev_id; > > > > - if (test_bit(I2C_HID_READ_PENDING, &ihid->flags)) > > - return IRQ_HANDLED; > > - > > i2c_hid_get_input(ihid); > > > > return IRQ_HANDLED; =20 >=20 > Patch applied cleanly on top of 6.7.9, builds OK (No warns, etc). >=20 > This indeed fixes the hang completely. Nice! I assume I can add Reported-and-tested-by: Eva Kurchatova to the patch? > I modified RVVM to send millions of keystroke events per second, > and put `reboot` as a service hook in the guest. It has been continuously > rebooting without a hitch for the last 30 minutes or so (Full boot takes > around 2 seconds), whereas unpatched 6.7.9 hangs almost immediately > in such conditions (Reverted your patch & rebuilt to be sure). >=20 > Thank you very much for this! Hope to see it upstreamed soon Thank you for the report, your investigation helped a lot. I am still confused why RT throttling doesn't unstuck the kernel in this case. I will consult some people and investigate more on this. But I think this patch is good on its own, so I will send a proper patch shortly. Best regards, Nam From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D2927C54E5D for ; Mon, 18 Mar 2024 09:01:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=WAZKZGN9gt7vo9/HiSbJWVkfZUfK34uv2ury1g3O0iU=; b=PtZmdOKNPmcGPd 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