On Thu, Oct 10, 2019 at 09:31:21AM +0200, Peter Zijlstra wrote: > On Wed, Oct 09, 2019 at 10:36:38PM -0400, Steven Rostedt wrote: > > From: Steven Rostedt (VMware) <rost...@goodmis.org> > > > > In the process of using text_poke_bp() for ftrace on x86, when > > performing the following action: > > > > # rmmod snd_hda_codec_hdmi > > # echo function > /sys/kernel/tracing/current_tracer > > # modprobe snd_hda_codec_hdmi > > > > It triggered this: > > > > BUG: unable to handle page fault for address: ffffffffa03d0000 > > #PF: supervisor write access in kernel mode > > #PF: error_code(0x0003) - permissions violation > > PGD 2a12067 P4D 2a12067 PUD 2a13063 PMD c42bc067 PTE c58a0061 > > Oops: 0003 [#1] PREEMPT SMP KASAN PTI > > CPU: 1 PID: 1182 Comm: modprobe Not tainted 5.4.0-rc2-test+ #50 > > Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 > > v03.03 07/14/2016 > > RIP: 0010:memcpy_erms+0x6/0x10 > > Code: 90 90 90 90 eb 1e 0f 1f 00 48 89 f8 48 89 d1 48 c1 e9 03 83 e2 07 f3 > > 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1 <f3> a4 c3 0f 1f > > 80 00 00 00 00 48 89 f8 48 83 fa 20 72 7e 40 38 fe > > RSP: 0018:ffff8880a10479e0 EFLAGS: 00010246 > > RAX: ffffffffa03d0000 RBX: ffffffffa03d0000 RCX: 0000000000000005 > > RDX: 0000000000000005 RSI: ffffffff8363e160 RDI: ffffffffa03d0000 > > RBP: ffff88807e9ec000 R08: fffffbfff407a001 R09: fffffbfff407a001 > > R10: fffffbfff407a000 R11: ffffffffa03d0004 R12: ffffffff8221f160 > > R13: ffffffffa03d0000 R14: ffff88807e9ec000 R15: ffffffffa0481640 > > FS: 00007eff92e28280(0000) GS:ffff8880d4840000(0000) > > knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: ffffffffa03d0000 CR3: 00000000a1048001 CR4: 00000000001606e0 > > Call Trace: > > ftrace_make_call+0x76/0x90 > > ftrace_module_enable+0x493/0x4f0 > > load_module+0x3a31/0x3e10 > > ? ring_buffer_read+0x70/0x70 > > ? module_frob_arch_sections+0x20/0x20 > > ? rb_commit+0xee/0x600 > > ? tracing_generic_entry_update+0xe1/0xf0 > > ? ring_buffer_unlock_commit+0xfb/0x220 > > ? 0xffffffffa0000061 > > ? __do_sys_finit_module+0x11a/0x1b0 > > __do_sys_finit_module+0x11a/0x1b0 > > ? __ia32_sys_init_module+0x40/0x40 > > ? ring_buffer_unlock_commit+0xfb/0x220 > > ? function_trace_call+0x179/0x260 > > ? __do_sys_finit_module+0x1b0/0x1b0 > > ? __do_sys_finit_module+0x1b0/0x1b0 > > ? do_syscall_64+0x58/0x1a0 > > do_syscall_64+0x68/0x1a0 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > RIP: 0033:0x7eff92f42efd > > > > The reason is that ftrace_module_enable() is called after the module > > has set its text to read-only. There's subtle reasons that this needs > > to be called afterward, and we need to continue to do so. > > Please explain.
Also, no. If you _have_ to modify code after, then you get to use text_poke_bp() instead of text_poke_early(). But first we need to document why this needs to be late. That's the crucial point and you forgot to explain.
