On Thu, Dec 19, 2024 at 11:57:40PM +0100, Paolo Bonzini wrote: > It could be as simple as this on the kernel side: [adding Jens for > a first look] Cc'ing his @kernel email; first message: https://lore.kernel.org/linux-kernel/20241108130737.126567-1-pbonzini@xxxxxxxxxx/ > =============== 8< =========== > From: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Subject: [PATCH] fs: proc: mark user and I/O workers as "kernel threads" > > A Rust library called "minijail" is looking at procfs to check if > the current task has multiple threads, and to prevent fork() if it > does. This is because fork() is in general ill-advised in > multi-threaded programs, for example if another thread might have > taken locks. > > However, this attempt falls afoul of kernel threads that are children > of the user process that they serve. These are not a problem when > forking, but they are still present in procfs. The library should > discard them, but there is currently no way for userspace to detect > PF_USER_WORKER or PF_IO_WORKER threads. > > The closest is the "Kthread" key in /proc/PID/task/TID/status. Extend > it instead of introducing another keyl tasks that are marked with > PF_USER_WORKER or PF_IO_WORKER are not kthreads, but they are close > enough for basically all intents and purposes. Yes, this looks good to me. But I also would have thought the original patch was safe too :). Hopefully nothing depends on the current value for these... there is often something making it difficult to have nice things. > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > diff --git a/fs/proc/array.c b/fs/proc/array.c > index 34a47fb0c57f..f702fb50c8ef 100644 > --- a/fs/proc/array.c > +++ b/fs/proc/array.c > @@ -221,7 +221,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns, > #endif > seq_putc(m, '\n'); > - seq_printf(m, "Kthread:\t%c\n", p->flags & PF_KTHREAD ? '1' : '0'); > + seq_printf(m, "Kthread:\t%c\n", p->flags & (PF_KTHREAD | PF_USER_WORKER | PF_IO_WORKER) ? '1' : '0'); > } > void render_sigset_t(struct seq_file *m, const char *header,UBLK_U_IO_REGISTER_ZC_RING
