Comment 25 for bug 1172094

I am not sure if it is still the same issue, but the last comments in this bug are very similar to what is reported in bug 55821.

A reproducible test case I could not find. It just happens during normal use, though a heavy load (suspend/resume) may trigger it quicker. It is hard to be really sure of this however.

This is on a Lenovo T410 with fedora 18 (note: I think 17 did not have this problem).

EE) BUG: triggered 'if (priv->num_active_touches > priv->num_slots)'
(EE) BUG: synaptics.c:3122 in UpdateTouchState()
(EE)
(EE) Backtrace:
(EE) 0: /usr/bin/X (xorg_backtrace+0x36) [0x46c496]
(EE) 1: /usr/lib64/xorg/modules/input/synaptics_drv.so (0x7fda46838000+0x2e97) [0x7fda4683ae97]
(EE) 2: /usr/lib64/xorg/modules/input/synaptics_drv.so (0x7fda46838000+0x4593) [0x7fda4683c593]
(EE) 3: /usr/lib64/xorg/modules/input/synaptics_drv.so (0x7fda46838000+0x6fd2) [0x7fda4683efd2]
(EE) 4: /usr/bin/X (0x400000+0x89747) [0x489747]
(EE) 5: /usr/bin/X (0x400000+0xb2e88) [0x4b2e88]
(EE) 6: /lib64/libpthread.so.0 (0x35ea800000+0xf000) [0x35ea80f000]
(EE) 7: /lib64/libc.so.6 (__select+0x13) [0x35ea0eb773]
(EE) 8: /usr/bin/X (WaitForSomething+0x190) [0x469a10]
(EE) 9: /usr/bin/X (0x400000+0x39301) [0x439301]
(EE) 10: /usr/bin/X (0x400000+0x280ba) [0x4280ba]
(EE) 11: /lib64/libc.so.6 (__libc_start_main+0xf5) [0x35ea021a05]
(EE) 12: /usr/bin/X (0x400000+0x283fd) [0x4283fd]
(EE)

(gdb) info symbol 0x2e97
UpdateTouchState.isra.12 + 167 in section .text of /usr/lib64/xorg/modules/input/synaptics_drv.so
(gdb) info symbol 0x4593
HandleState + 499 in section .text of /usr/lib64/xorg/modules/input/synaptics_drv.so
(gdb) info symbol 0x6fd2
ReadInput + 130 in section .text of /usr/lib64/xorg/modules/input/synaptics_drv.so

(gdb) info symbol 0x489747
xf86SigioReadInput + 39 in section .text of /usr/bin/X
(gdb) info symbol 0x4b2e88
xf86SIGIO + 440 in section .text of /usr/bin/X

Touchpad is locked into "scrolling". A possible solution is probably to not increase num_active_touches if priv->num_active_touches > priv->num_slots.
But this would obviously not fix the underlying cause (just fix the annoying loss of trackpad).