On Tue 18-12-18 10:53:58, Vineet Gupta wrote: > Use on-stack smaller buffers instead of dynamic pages. > > The motivation for this change was to address lockdep splat when > signal handling code calls show_regs (with preemption disabled) and > ARC show_regs calls into sleepable page allocator. > > | potentially unexpected fatal signal 11. > | BUG: sleeping function called from invalid context at ../mm/page_alloc.c:4317 > | in_atomic(): 1, irqs_disabled(): 0, pid: 57, name: segv > | no locks held by segv/57. > | Preemption disabled at: > | [<8182f17e>] get_signal+0x4a6/0x7c4 > | CPU: 0 PID: 57 Comm: segv Not tainted 4.17.0+ #23 > | > | Stack Trace: > | arc_unwind_core.constprop.1+0xd0/0xf4 > | __might_sleep+0x1f6/0x234 > | __get_free_pages+0x174/0xca0 > | show_regs+0x22/0x330 > | get_signal+0x4ac/0x7c4 # print_fatal_signals() -> preempt_disable() > | do_signal+0x30/0x224 > | resume_user_mode_begin+0x90/0xd8 > > Despite this, lockdep still barfs (see next change), but this patch > still has merit as in we use smaller/localized buffers now and there's > less instructoh trace to sift thru when debugging pesky issues. But show_regs is called from contexts which might be called from deep call chains (e.g WARN). Is it safe to allocate such a large stack there? -- Michal Hocko SUSE Labs
