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SubjectRe: ipv6: tunnel: hang when destroying ipv6 tunnel
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Sasha Levin wrote:
> While it seems that 9p is the culprit, I have to point out that this
> bug is easily reproducible, and it happens each time due to a
> call_usermode_helper() call. Other than that 9p behaves perfectly and
> I'd assume that I'd be seeing other things break besides
> call_usermode_helper() related ones.

I think one of below two patches can catch the bug if this is a usermodehelper
related bug. Please try.

----- Patch 1 -----
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 01394b6..3e63319 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -571,7 +571,7 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
* flag, for khelper thread is already waiting for the thread at
* wait_for_completion() in do_fork().
*/
- if (wait != UMH_NO_WAIT && current == kmod_thread_locker) {
+ if (WARN_ON(wait != UMH_NO_WAIT && current == kmod_thread_locker)) {
retval = -EBUSY;
goto out;
}

----- Patch 2 -----
diff --git a/include/linux/kmod.h b/include/linux/kmod.h
index 9efeae6..1350670 100644
--- a/include/linux/kmod.h
+++ b/include/linux/kmod.h
@@ -48,10 +48,10 @@ static inline int request_module_nowait(const char *name, ...) { return -ENOSYS;
struct cred;
struct file;

-#define UMH_NO_WAIT 0 /* don't wait at all */
-#define UMH_WAIT_EXEC 1 /* wait for the exec, but not the process */
-#define UMH_WAIT_PROC 2 /* wait for the process to complete */
-#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */
+#define UMH_NO_WAIT 0x10 /* don't wait at all */
+#define UMH_WAIT_EXEC 0x11 /* wait for the exec, but not the process */
+#define UMH_WAIT_PROC 0x12 /* wait for the process to complete */
+#define UMH_KILLABLE 0x04 /* wait for EXEC/PROC killable */

struct subprocess_info {
struct work_struct work;
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 957a7aa..ecfd3d5 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -483,6 +483,18 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
DECLARE_COMPLETION_ONSTACK(done);
int retval = 0;

+ if (unlikely(wait == -1 || wait == 0 || wait == 1)) {
+ WARN(1, "Requesting for usermode helper with hardcoded wait "
+ "flag. Change to use UMH_* symbols and recompile, or "
+ "this request will fail on Linux 3.4.\n");
+ if (wait == -1)
+ wait = UMH_NO_WAIT;
+ else if (wait == 0)
+ wait = UMH_WAIT_EXEC;
+ else
+ wait = UMH_WAIT_PROC;
+ }
+
helper_lock();
if (sub_info->path[0] == '\0')
goto out;

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