This is a note to let you know that I've just added the patch titled
x86/process: setup io_threads more like normal user space threads
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-process-setup-io_threads-more-like-normal-user-space-threads.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f757cc1efe0ec578f54dc857f1684dcd6541b464 Mon Sep 17 00:00:00 2001
From: Stefan Metzmacher <metze@xxxxxxxxx>
Date: Wed, 5 May 2021 13:03:10 +0200
Subject: x86/process: setup io_threads more like normal user space threads
From: Stefan Metzmacher <metze@xxxxxxxxx>
[ Upstream commit 50b7b6f29de3e18e9d6c09641256a0296361cfee ]
As io_threads are fully set up USER threads it's clearer to separate the
code path from the KTHREAD logic.
The only remaining difference to user space threads is that io_threads
never return to user space again. Instead they loop within the given
worker function.
The fact that they never return to user space means they don't have an
user space thread stack. In order to indicate that to tools like gdb we
reset the stack and instruction pointers to 0.
This allows gdb attach to user space processes using io-uring, which like
means that they have io_threads, without printing worrying message like
this:
warning: Selected architecture i386:x86-64 is not compatible with reported target architecture i386
warning: Architecture rejected target-supplied description
The output will be something like this:
(gdb) info threads
Id Target Id Frame
* 1 LWP 4863 "io_uring-cp-for" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
2 LWP 4864 "iou-mgr-4863" 0x0000000000000000 in ?? ()
3 LWP 4865 "iou-wrk-4863" 0x0000000000000000 in ?? ()
(gdb) thread 3
[Switching to thread 3 (LWP 4865)]
#0 0x0000000000000000 in ?? ()
(gdb) bt
#0 0x0000000000000000 in ?? ()
Backtrace stopped: Cannot access memory at address 0x0
Fixes: 4727dc20e042 ("arch: setup PF_IO_WORKER threads like PF_KTHREAD")
Link: https://lore.kernel.org/io-uring/044d0bad-6888-a211-e1d3-159a4aeed52d@xxxxxxxxxx/T/#m1bbf5727e3d4e839603f6ec7ed79c7eebfba6267
Signed-off-by: Stefan Metzmacher <metze@xxxxxxxxx>
cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Andy Lutomirski <luto@xxxxxxxxxx>
cc: linux-kernel@xxxxxxxxxxxxxxx
cc: io-uring@xxxxxxxxxxxxxxx
cc: x86@xxxxxxxxxx
Link: https://lore.kernel.org/r/20210505110310.237537-1-metze@xxxxxxxxx
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/process.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -162,7 +162,7 @@ int copy_thread(unsigned long clone_flag
#endif
/* Kernel thread ? */
- if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+ if (unlikely(p->flags & PF_KTHREAD)) {
memset(childregs, 0, sizeof(struct pt_regs));
kthread_frame_init(frame, sp, arg);
return 0;
@@ -178,6 +178,23 @@ int copy_thread(unsigned long clone_flag
task_user_gs(p) = get_user_gs(current_pt_regs());
#endif
+ if (unlikely(p->flags & PF_IO_WORKER)) {
+ /*
+ * An IO thread is a user space thread, but it doesn't
+ * return to ret_after_fork().
+ *
+ * In order to indicate that to tools like gdb,
+ * we reset the stack and instruction pointers.
+ *
+ * It does the same kernel frame setup to return to a kernel
+ * function that a kernel thread does.
+ */
+ childregs->sp = 0;
+ childregs->ip = 0;
+ kthread_frame_init(frame, sp, arg);
+ return 0;
+ }
+
/* Set a new TLS for the child thread? */
if (clone_flags & CLONE_SETTLS)
ret = set_new_tls(p, tls);
Patches currently in stable-queue which might be from metze@xxxxxxxxx are
queue-5.10/x86-process-setup-io_threads-more-like-normal-user-space-threads.patch
