Hi
On Thu, Nov 16, 2023 at 3:54 PM Nicholas Piggin <npiggin@gmail.com> wrote:
If a chardev socket is not read, it will eventually fill and QEMU
can block attempting to write to it. A difficult bug in avocado
tests where the console socket was not being read from caused this
hang.
warn if a chardev write is blocked for 100ms.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
This is not necessary for the fix but it does trigger in the
failing avocado test without the previous patch applied. Maybe
it would be helpful?
Thanks,
Nick
chardev/char.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/chardev/char.c b/chardev/char.c
index 996a024c7a..7c375e3cc4 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -114,6 +114,8 @@ static int qemu_chr_write_buffer(Chardev *s,
{
ChardevClass *cc = CHARDEV_GET_CLASS(s);
int res = 0;
+ int nr_retries = 0;
+
*offset = 0;
qemu_mutex_lock(&s->chr_write_lock);
@@ -126,6 +128,10 @@ static int qemu_chr_write_buffer(Chardev *s,
} else {
g_usleep(100);
}
+ if (++nr_retries == 1000) { /* 100ms */
+ warn_report("Chardev '%s' write blocked for > 100ms, "
+ "socket buffer full?", s->label);
+ }
That shouldn't happen, the frontend should poll and only write when it
can. What is the qemu command being used here?