um: Rewrite the sigio workaround based on epoll and tgkill

The existing sigio workaround implementation removes FDs from the
poll when events are triggered, requiring users to re-add them via
add_sigio_fd() after processing. This introduces a potential race
condition between FD removal in write_sigio_thread() and next_poll
update in __add_sigio_fd(), and is inefficient due to frequent FD
removal and re-addition. Rewrite the implementation based on epoll
and tgkill for improved efficiency and reliability.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20250315161910.4082396-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 0 insertions, 26 deletions

diff --git a/arch/um/kernel/sigio.c b/arch/um/kernel/sigio.c
index 5085a50c3b8c..4fc04742048a 100644
--- a/arch/um/kernel/sigio.c
+++ b/arch/um/kernel/sigio.c
@@ -8,32 +8,6 @@
 #include <os.h>
 #include <sigio.h>
 
-/* Protected by sigio_lock() called from write_sigio_workaround */
-static int sigio_irq_fd = -1;
-
-static irqreturn_t sigio_interrupt(int irq, void *data)
-{
-	char c;
-
-	os_read_file(sigio_irq_fd, &c, sizeof(c));
-	return IRQ_HANDLED;
-}
-
-int write_sigio_irq(int fd)
-{
-	int err;
-
-	err = um_request_irq(SIGIO_WRITE_IRQ, fd, IRQ_READ, sigio_interrupt,
-			     0, "write sigio", NULL);
-	if (err < 0) {
-		printk(KERN_ERR "write_sigio_irq : um_request_irq failed, "
-		       "err = %d\n", err);
-		return -1;
-	}
-	sigio_irq_fd = fd;
-	return 0;
-}
-
 /* These are called from os-Linux/sigio.c to protect its pollfds arrays. */
 static DEFINE_MUTEX(sigio_mutex);