linux-kernel - Re: pcie: xilinx: kernel hang

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Date:   Wed, 8 Jan 2020 20:03:02 +0530
From:   Muni Sekhar <munisekharrms@...il.com>
To:     linux-pci@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: pcie: xilinx: kernel hang - ISR readl()

On Tue, Jan 7, 2020 at 9:45 PM Muni Sekhar <munisekharrms@...il.com> wrote:
>
> Hi,
>
> I have module with Xilinx FPGA. It implements UART(s), SPI(s),
> parallel I/O and interfaces them to the Host CPU via PCI Express bus.
> I see that my system freezes without capturing the crash dump for
> certain tests. I debugged this issue and it was tracked down to the
> below mentioned interrupt handler code.
>
>
> In ISR, first reads the Interrupt Status register using ‘readl()’ as
> given below.
>     status = readl(ctrl->reg + INT_STATUS);
>
>
> And then clears the pending interrupts using ‘writel()’ as given blow.
>         writel(status, ctrl->reg + INT_STATUS);
>
>
> I've noticed a kernel hang if INT_STATUS register read again after
> clearing the pending interrupts.
>
> Can someone clarify me why the kernel hangs without crash dump incase
> if I read the INT_STATUS register using readl() after clearing the
> pending bits?
>
> Can readl() block?
>
>
> Snippet of the ISR code is given blow:
>
> https://pastebin.com/WdnZJZF5
The correct snippet of the ISR code is here: https://pastebin.com/as2tSPwE
>
>
>
> static irqreturn_t pcie_isr(int irq, void *dev_id)
>
> {
>
>         struct test_device *ctrl = data;
>
>         u32 status;
>
> …
>
>
>
>         status = readl(ctrl->reg + INT_STATUS);
>
>         /*
>
>          * Check to see if it was our interrupt
>
>          */
>
>         if (!(status & 0x000C))
>
>                 return IRQ_NONE;
>
>
>
>         /* Clear the interrupt */
>
>         writel(status, ctrl->reg + INT_STATUS);
>
>
>
>         if (status & 0x0004) {
>
>                 /*
>
>                  * Tx interrupt pending.
>
>                  */
>
>                  ....
>
>        }
>
>
>
>         if (status & 0x0008) {
>
>                 /* Rx interrupt Pending */
>
>                 /* The system freezes if I read again the INT_STATUS
> register as given below */
>
>                 status = readl(ctrl->reg + INT_STATUS);
>
>                 ....
>
>         }
>
> ..
>
>         return IRQ_HANDLED;
> }
>
>
>
> --
> Thanks,
> Sekhar



-- 
Thanks,
Sekhar