Bug#1005900: linux.uml: uml_mconsole client becomes blocked on read after issuing commands stop and go

[Ritesh Raj Sarraf]

Hello Mihai,

In this case, it is good to have the User Mode Linux upstream in the
loop.

Thanks,
Ritesh

--- linux-source-5.16/arch/um/drivers/mconsole_kern.c	2022-02-05 20:22:06.000000000 +0200
+++ linux-source-5.16.fix/arch/um/drivers/mconsole_kern.c	2022-02-16 23:35:39.562668086 +0200
@@ -224,6 +224,7 @@
 
 void mconsole_stop(struct mc_request *req)
 {
+	int err;
 	deactivate_fd(req->originating_fd, MCONSOLE_IRQ);
 	os_set_fd_block(req->originating_fd, 1);
 	mconsole_reply(req, "stopped", 0, 0);
@@ -247,6 +248,11 @@
 	}
 	os_set_fd_block(req->originating_fd, 0);
 	mconsole_reply(req, "", 0, 0);
+	err=activate_fd(MCONSOLE_IRQ, req->originating_fd, IRQ_READ,
+		(void*)(req->originating_fd), NULL);
+	if (err)
+	  mconsole_reply(req, "Failed to reactivate MCONSOLE_IRQ, \
+			this will block the read for uml_mconsole", 1, 0);
 }
 
 static DEFINE_SPINLOCK(mc_devices_lock);
--- linux-source-5.16/arch/um/kernel/irq.c	2022-02-05 20:22:06.000000000 +0200
+++ linux-source-5.16.fix/arch/um/kernel/irq.c	2022-02-16 23:39:15.650279367 +0200
@@ -249,7 +249,7 @@
 		free_irq_entry(entry, false);
 }
 
-static int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id,
+int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id,
 		       void (*timetravel_handler)(int, int, void *,
 						  struct time_travel_event *))
 {
@@ -304,6 +304,7 @@
 out:
 	return err;
 }
+EXPORT_SYMBOL(activate_fd);
 
 /*
  * Remove the entry or entries for a specific FD, if you
--- linux-source-5.16/arch/um/include/shared/irq_user.h	2022-02-05 20:22:06.000000000 +0200
+++ linux-source-5.16.fix/arch/um/include/shared/irq_user.h	2022-02-16 23:39:09.642292312 +0200
@@ -19,6 +19,7 @@
 void sigio_run_timetravel_handlers(void);
 extern void free_irq_by_fd(int fd);
 extern void deactivate_fd(int fd, int irqnum);
+extern int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id, void (*timetravel_handler)(int, int, void *, struct time_travel_event *));
 extern int deactivate_all_fds(void);
 extern int activate_ipi(int fd, int pid);

On Thu, 2022-02-17 at 01:06 +0200, Mihai Hanor wrote:
> Package: user-mode-linux
> Version: 5.16um1
> Severity: normal
> File: /usr/bin/linux.uml
> X-Debbugs-Cc: quake2iasi at gmail.com
> 
> Dear Maintainer,
> 
> * What is the problem:
> Issuing the commands stop followed by go, at the input of the
> uml_mconsole
> client, results in the client becoming blocked on read socket. This
> is because
> of logic in arch/um/drivers/mconsole_kern.c, where mconsole_stop()
> doesn't
> reactivate the MCONSOLE_IRQ before the function has exited.
> 
> I've managed to find a fix which seems to be working, but I don't
> know if it's
> a proper fix. Please see the attached file.
> 
> 
> -- System Information:
> Debian Release: bookworm/sid
>   APT prefers testing
>   APT policy: (900, 'testing'), (500, 'unstable-debug'), (500,
> 'testing-debug'), (1, 'unstable')
> Architecture: amd64 (x86_64)
> Foreign Architectures: i386
> 
> Kernel: Linux 5.16.0-1-amd64 (SMP w/4 CPU threads; PREEMPT)
> Kernel taint flags: TAINT_WARN
> Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8),
> LANGUAGE=en_US:en
> Shell: /bin/sh linked to /bin/dash
> Init: systemd (via /run/systemd/system)
> LSM: AppArmor: enabled
> 
> Versions of packages user-mode-linux depends on:
> ii  libc6  2.33-5
> 
> Versions of packages user-mode-linux recommends:
> ii  uml-utilities  20070815.4-1
> 
> Versions of packages user-mode-linux suggests:
> ii  mate-terminal [x-terminal-emulator]  1.26.0-1
> ii  pterm [x-terminal-emulator]          0.76-2
> pn  rootstrap                            <none>
> pn  slirp                                <none>
> pn  user-mode-linux-doc                  <none>
> pn  vde2                                 <none>
> 
> -- no debconf information

-- 
Ritesh Raj Sarraf | http://people.debian.org/~rrs
Debian - The Universal Operating System
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