[Skiboot] [PATCH 1/4] fsp/console: Ignore data on unresponsive consoles
Samuel Mendoza-Jonas
sam at mendozajonas.com
Thu Jul 14 10:26:00 AEST 2016
On Tue, 2016-06-28 at 13:07 +1000, Samuel Mendoza-Jonas wrote:
> Linux kernels from v4.1 onwards will try to request an irq for each hvc
> console using OPAL_EVENT_CONSOLE_INPUT, however because the IRQF_SHARED
> flag is not set any console after the first will fail. If there is data
> on one of these failed consoles OPAL will set OPAL_EVENT_CONSOLE_INPUT
> every time fsp_console_read is called, leading to RCU stalls in the
> kernel.
>
> As a workaround for unpatched kernels, cease setting
> OPAL_EVENT_CONSOLE_INPUT for consoles that we have noticed are not being
> read.
>
> Signed-off-by: Samuel Mendoza-Jonas <sam at mendozajonas.com>
Realised I forgot to mention, patch 1 in particular should be merged into
stable as well.
> ---
> hw/fsp/fsp-console.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/hw/fsp/fsp-console.c b/hw/fsp/fsp-console.c
> index 2a25e1c..87e509d 100644
> --- a/hw/fsp/fsp-console.c
> +++ b/hw/fsp/fsp-console.c
> @@ -54,6 +54,7 @@ struct fsp_serial {
> struct fsp_serbuf_hdr *in_buf;
> struct fsp_serbuf_hdr *out_buf;
> struct fsp_msg *poke_msg;
> + u8 waiting;
> };
>
> #define SER_BUFFER_SIZE 0x00040000UL
> @@ -653,6 +654,8 @@ static int64_t fsp_console_read(int64_t term_number, int64_t *length,
> unlock(&fsp_con_lock);
> return OPAL_CLOSED;
> }
> + if (fs->waiting)
> + fs->waiting = 0;
> sb = fs->in_buf;
> old_nin = sb->next_in;
> lwsync();
> @@ -687,8 +690,19 @@ static int64_t fsp_console_read(int64_t term_number, int64_t *length,
>
> if (fs->log_port || !fs->open)
> continue;
> - if (sb->next_out != sb->next_in)
> - pending = true;
> + if (sb->next_out != sb->next_in) {
> + /*
> + * HACK: Some kernels (4.1+) may fail to properly
> + * register hvc1 and will never read it. This can lead
> + * to RCU stalls, so if we notice this console is not
> + * being read, do not set OPAL_EVENT_CONSOLE_INPUT even
> + * if it has data
> + */
> + if (fs->waiting < 5) {
> + pending = true;
> + fs->waiting++;
> + }
> + }
> }
> if (!pending)
> opal_update_pending_evt(OPAL_EVENT_CONSOLE_INPUT, 0);
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