Created attachment 132506 [details]
I noticed a bug on my lenovo yoga 2 13 laptop. Seemingly random the x server kind of dies : it slows down really hard until I cannot do anything and have to force a restart. Here's the important part of the stacktrace :
[117119.110] (EE) BUG: triggered 'if (priv->num_active_touches == 0)'
[117119.110] (EE) BUG: ../../src/synaptics.c:2958 in UpdateTouchState()
[117119.110] (EE) Backtrace:
[117119.111] (EE) 0: /usr/lib/xorg/Xorg (xorg_backtrace+0x4a) [0x56003cf28c8a]
[117119.111] (EE) 1: /usr/lib/xorg/modules/input/synaptics_drv.so (0x7f446b311000+0x4914) [0x7f446b315914]
[117119.111] (EE) 2: /usr/lib/xorg/modules/input/synaptics_drv.so (0x7f446b311000+0x6802) [0x7f446b317802]
[117119.111] (EE) 3: /usr/lib/xorg/Xorg (0x56003cd70000+0x1badfc) [0x56003cf2adfc]
[117119.111] (EE) 4: /usr/lib/xorg/Xorg (0x56003cd70000+0x1bd501) [0x56003cf2d501]
[117119.111] (EE) 5: /usr/lib/xorg/Xorg (0x56003cd70000+0x1bac56) [0x56003cf2ac56]
[117119.111] (EE) 6: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7f4474cf0000+0x76da) [0x7f4474cf76da]
[117119.111] (EE) 7: /lib/x86_64-linux-gnu/libc.so.6 (clone+0x5f) [0x7f4474a3117f]
Note that this is a backtrace identifying a bug but not a crash - the backtrace simply intends to make finding the bug easier. It's a well-known but so far unidentified issue but so far has not lead to crashes.
in other words, it's unlikely to be the source of the slowdown/crash. I recommend trying xf86-input-libinput instead of synaptics though, if it still happens then it's definitely unrelated to synaptics.