On 01/25, Srikar Dronamraju wrote: > > > The uprobes is_trap_at_addr() location holds mmap_sem and > > calls get_user_pages(current->mm) on an instruction address. This > > makes it a pretty unique gup caller. Yes, in particular is_trap_at_addr() doesn't look really nice. But we need to read the insn under mmap_sem to avoid the race with unregister + register at the same address, so that we won't send the wrong SIGTRAP in this case. > Changes for uprobes.c looks good to me. > Acked-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> Agreed, the changes in uprobes.c look fine. > > @@ -1700,7 +1700,13 @@ static int is_trap_at_addr(struct mm_str > > if (likely(result == 0)) > > goto out; > > > > - result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL); > > + /* > > + * The NULL 'tsk' here ensures that any faults that occur here > > + * will not be accounted to the task. 'mm' *is* current->mm, > > + * but we treat this as a 'foreign' access since it is > > + * essentially a kernel access to the memory. > > + */ > > + result = get_user_pages_foreign(NULL, mm, vaddr, 1, 0, 1, &page, NULL); > > if (result < 0) > > return result; Yes, but perhaps we should simply remove this get_user_pages_foreign() and just return -EFAULT if copy_from_user_inatomic() fails. This should be very unlikely case, I think it would be fine to restart this insn and take another bp hit to fault this page in. Srikar what do you think? IIRC, this get_user_pages() was needed before, when is_trap_at_addr() had other (non-restartable) callers with mm != current->mm. But again, I think this patch is fine, we can do this later. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>