On Mon, Dec 21, 2015 at 12:50 PM, Sasha Levin <[email protected]> wrote: > On 07/03/2015 03:44 PM, Andy Lutomirski wrote: >> Changing the x86 context tracking hooks is dangerous because there >> are no good checks that we track our context correctly. Add a >> helper to check that we're actually in CONTEXT_USER when we enter >> from user mode and wire it up for syscall entries. >> >> Subsequent patches will wire this up for all non-NMI entries as >> well. NMIs are their own special beast and cannot currently switch >> overall context tracking state. Instead, they have their own >> special RCU hooks. >> >> This is a tiny speedup if !CONFIG_CONTEXT_TRACKING (removes a >> branch) and a tiny slowdown if CONFIG_CONTEXT_TRACING (adds a layer >> of indirection). Eventually, we should fix up the core context >> tracking code to supply a function that does what we want (and can >> be much simpler than user_exit), which will enable us to get rid of >> the extra call. > > Hey Andy, > > I see the following warning in today's -next:
Weird. I wonder if you might have hit this while switching context tracking on a runtime. (Can you even do that?) --Andy > > [ 2162.706868] ------------[ cut here ]------------ > [ 2162.708021] WARNING: CPU: 4 PID: 28801 at arch/x86/entry/common.c:44 > enter_from_user_mode+0x1c/0x50() > [ 2162.709466] Modules linked in: > [ 2162.709998] CPU: 4 PID: 28801 Comm: trinity-c375 Tainted: G B > 4.4.0-rc5-next-20151221-sasha-00020-g840272e-dirty #2753 > [ 2162.711847] 0000000000000000 00000000f17e6fcd ffff880292d5fe08 > ffffffffa4045334 > [ 2162.713108] 0000000041b58ab3 ffffffffaf66686b ffffffffa4045289 > ffff880292d5fdc0 > [ 2162.714544] 0000000000000000 00000000f17e6fcd ffffffffa23cf466 > 0000000000000004 > [ 2162.715793] Call Trace: > [ 2162.716229] dump_stack (lib/dump_stack.c:52) > [ 2162.719021] warn_slowpath_common (kernel/panic.c:484) > [ 2162.721014] warn_slowpath_null (kernel/panic.c:518) > [ 2162.721950] enter_from_user_mode (arch/x86/entry/common.c:44 > (discriminator 7) include/linux/context_tracking_state.h:30 (discriminator 7) > include/linux/context_tracking.h:30 (discriminator 7) > arch/x86/entry/common.c:45 (discriminator 7)) > [ 2162.722911] syscall_trace_enter_phase1 (arch/x86/entry/common.c:94) > [ 2162.726914] tracesys (arch/x86/entry/entry_64.S:241) > [ 2162.727704] ---[ end trace 1e5b49c361cbfe8b ]--- > [ 2162.728468] BUG: scheduling while atomic: trinity-c375/28801/0x00000401 > [ 2162.729517] Modules linked in: > [ 2162.730020] Preemption disabled param_attr_store (kernel/params.c:625) > [ 2162.731304] > [ 2162.731579] CPU: 4 PID: 28801 Comm: trinity-c375 Tainted: G B W > 4.4.0-rc5-next-20151221-sasha-00020-g840272e-dirty #2753 > [ 2162.733432] 0000000000000000 00000000f17e6fcd ffff880292d5fe20 > ffffffffa4045334 > [ 2162.734778] 0000000041b58ab3 ffffffffaf66686b ffffffffa4045289 > ffff880292d5fde0 > [ 2162.736036] fffffffface198f9 00000000f17e6fcd ffff880292d5fe50 > 0000000000000282 > [ 2162.737309] Call Trace: > [ 2162.737718] dump_stack (lib/dump_stack.c:52) > [ 2162.740566] __schedule_bug (kernel/sched/core.c:3102) > [ 2162.741498] __schedule (./arch/x86/include/asm/preempt.h:27 > kernel/sched/core.c:3116 kernel/sched/core.c:3225) > [ 2162.742391] schedule (kernel/sched/core.c:3312 (discriminator 1)) > [ 2162.743221] exit_to_usermode_loop (arch/x86/entry/common.c:246) > [ 2162.744331] syscall_return_slowpath (arch/x86/entry/common.c:282 > include/linux/context_tracking_state.h:30 include/linux/context_tracking.h:24 > arch/x86/entry/common.c:284 arch/x86/entry/common.c:344) > [ 2162.745364] int_ret_from_sys_call (arch/x86/entry/entry_64.S:282) > > > Thanks, > Sasha -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
