Discussion:
[PATCH] powerpc/udbg_hvc: retry putc on -EAGAIN
Nathan Lynch
2021-05-14 21:44:22 UTC
Permalink
hvterm_raw_put_chars() calls hvc_put_chars(), which may return -EAGAIN
when the underlying hcall returns a "busy" status, but udbg_hvc_putc()
doesn't handle this. When using xmon on a PowerVM guest, this can
result in incomplete or garbled output when printing relatively large
amounts of data quickly, such as when dumping the kernel log buffer.

Call again on -EAGAIN.

Signed-off-by: Nathan Lynch <***@linux.ibm.com>
---
drivers/tty/hvc/hvc_vio.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/hvc/hvc_vio.c b/drivers/tty/hvc/hvc_vio.c
index 798f27f40cc2..76d2a7038095 100644
--- a/drivers/tty/hvc/hvc_vio.c
+++ b/drivers/tty/hvc/hvc_vio.c
@@ -249,7 +249,7 @@ static void udbg_hvc_putc(char c)
count = hvterm_hvsi_put_chars(0, &c, 1);
break;
}
- } while(count == 0);
+ } while(count == 0 || count == -EAGAIN);
}

static int udbg_hvc_getc_poll(void)
--
2.30.2
Greg KH
2021-05-21 12:47:36 UTC
Permalink
Post by Nathan Lynch
hvterm_raw_put_chars() calls hvc_put_chars(), which may return -EAGAIN
when the underlying hcall returns a "busy" status, but udbg_hvc_putc()
doesn't handle this. When using xmon on a PowerVM guest, this can
result in incomplete or garbled output when printing relatively large
amounts of data quickly, such as when dumping the kernel log buffer.
Call again on -EAGAIN.
---
drivers/tty/hvc/hvc_vio.c | 2 +-
Subject line does not match up with this file name.

Don't you want "tty" and "hvc" in there somewhere?

thanks,

greg k-h
Michael Ellerman
2021-05-23 10:51:09 UTC
Permalink
Post by Greg KH
Post by Nathan Lynch
hvterm_raw_put_chars() calls hvc_put_chars(), which may return -EAGAIN
when the underlying hcall returns a "busy" status, but udbg_hvc_putc()
doesn't handle this. When using xmon on a PowerVM guest, this can
result in incomplete or garbled output when printing relatively large
amounts of data quickly, such as when dumping the kernel log buffer.
Call again on -EAGAIN.
---
drivers/tty/hvc/hvc_vio.c | 2 +-
Subject line does not match up with this file name.
Don't you want "tty" and "hvc" in there somewhere?
It's a powerpc only driver, but I guess the subject should still be
"tty: hvc: ..." to match convention.

I was planning to take this via the powerpc tree, but I can drop it if
you'd rather take it.

cheers
Greg KH
2021-05-27 11:10:23 UTC
Permalink
Post by Michael Ellerman
Post by Greg KH
Post by Nathan Lynch
hvterm_raw_put_chars() calls hvc_put_chars(), which may return -EAGAIN
when the underlying hcall returns a "busy" status, but udbg_hvc_putc()
doesn't handle this. When using xmon on a PowerVM guest, this can
result in incomplete or garbled output when printing relatively large
amounts of data quickly, such as when dumping the kernel log buffer.
Call again on -EAGAIN.
---
drivers/tty/hvc/hvc_vio.c | 2 +-
Subject line does not match up with this file name.
Don't you want "tty" and "hvc" in there somewhere?
It's a powerpc only driver, but I guess the subject should still be
"tty: hvc: ..." to match convention.
I was planning to take this via the powerpc tree, but I can drop it if
you'd rather take it.
No problem, feel free to take it yourself!

greg k-h
Michael Ellerman
2021-06-06 12:08:38 UTC
Permalink
Post by Nathan Lynch
hvterm_raw_put_chars() calls hvc_put_chars(), which may return -EAGAIN
when the underlying hcall returns a "busy" status, but udbg_hvc_putc()
doesn't handle this. When using xmon on a PowerVM guest, this can
result in incomplete or garbled output when printing relatively large
amounts of data quickly, such as when dumping the kernel log buffer.
Call again on -EAGAIN.
Applied to powerpc/next.

[1/1] powerpc/udbg_hvc: retry putc on -EAGAIN
https://git.kernel.org/powerpc/c/027f55e87c3094270a3223f7331d033fe15a2b3f

cheers

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