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authorStefan Metzmacher <metze@samba.org>2021-05-05 13:03:10 +0200
committerJens Axboe <axboe@kernel.dk>2021-05-05 17:47:41 -0600
commit50b7b6f29de3e18e9d6c09641256a0296361cfee (patch)
tree0f1f7e713aee5944cca46448a3da78e16aeca343
parenta5e7da1494e191c561ecce8829a6c19449585e3d (diff)
x86/process: setup io_threads more like normal user space threads
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@polymtl.ca/T/#m1bbf5727e3d4e839603f6ec7ed79c7eebfba6267 Signed-off-by: Stefan Metzmacher <metze@samba.org> cc: Linus Torvalds <torvalds@linux-foundation.org> cc: Jens Axboe <axboe@kernel.dk> cc: Andy Lutomirski <luto@kernel.org> cc: linux-kernel@vger.kernel.org cc: io-uring@vger.kernel.org cc: x86@kernel.org Link: https://lore.kernel.org/r/20210505110310.237537-1-metze@samba.org Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--arch/x86/kernel/process.c19
1 files changed, 18 insertions, 1 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 43cbfc84153a..5e1f38179f49 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -156,7 +156,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
#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;
@@ -172,6 +172,23 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
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);