Comment 15 for bug 1203273

with O0 -g3 it was not so easy to trigger, but:

Program received signal SIGSEGV, Segmentation fault.
0x00007f1472b8b88c in has_offload_slaves (sna=0x7f1471868000)
    at sna_accel.c:14747
14747 ScreenPtr screen = sna->scrn->pScreen;
(gdb) bt full
#0 0x00007f1472b8b88c in has_offload_slaves (sna=0x7f1471868000)
    at sna_accel.c:14747
        screen = 0x2085620
        dirty = 0x7fff0733c890
#1 0x00007f1472b8ba3b in stop_flush (sna=0x7f1471868000, scanout=0x207aa60)
    at sna_accel.c:14810
No locals.
#2 0x00007f1472b8c1bf in sna_accel_flush (sna=0x7f1471868000)
    at sna_accel.c:15032
        priv = 0x207aa60
        busy = false
#3 0x00007f1472b8cf29 in sna_accel_block_handler (sna=0x7f1471868000,
    tv=0x7fff0733c998) at sna_accel.c:15472
No locals.
#4 0x00007f1472ba67d8 in sna_block_handler (arg=0x2054420,
    timeout=0x7fff0733c998, read_mask=0x81c340 <LastSelectMask>)
    at sna_driver.c:557
        sna = 0x7f1471868000
        tv = 0x7fff0733c998
#5 0x000000000043d9c4 in BlockHandler (
    pTimeout=pTimeout@entry=0x7fff0733c998,
    pReadmask=pReadmask@entry=0x81c340 <LastSelectMask>) at dixutils.c:387
        i = 0
---Type <return> to continue, or q <return> to quit---
        j = <optimized out>
#6 0x0000000000469e84 in WaitForSomething (
    pClientsReady=pClientsReady@entry=0x22e29d0) at WaitFor.c:210
        i = <optimized out>
        waittime = {tv_sec = 296, tv_usec = 432000}
        wt = 0x7fff0733c9a0
        timeout = <optimized out>
        clientsReadable = {fds_bits = {0 <repeats 16 times>}}
        clientsWritable = {fds_bits = {1, 1, 0, 34103520, 0, 0, 33899552,
            5413855, 33899552, 46103504, 77595664, 206158430224,
            140733314222960, 140733314222752, 46041312, 264619602646}}
        selecterr = <optimized out>
        nready = 0
        devicesReadable = {fds_bits = {57, 1, 140733314222912, 32, 46103344,
            4689382, 32, 46103344, 51602000, 4651885, 0, 32, 0, 0, 0,
            46103440}}
        now = <optimized out>
        someReady = 0
#7 0x0000000000439581 in Dispatch () at dispatch.c:357
        clientReady = 0x22e29d0
        result = <optimized out>
        client = <optimized out>
        nready = <optimized out>
---Type <return> to continue, or q <return> to quit---
        icheck = 0x8163f0 <checkForInput>
        start_tick = <optimized out>
#8 0x00000000004282da in main (argc=9, argv=0x7fff0733cda8,
    envp=<optimized out>) at main.c:298
        i = <optimized out>
        alwaysCheckForInput = {0, 1}
(gdb)

Valgrind will have to wait until tomorrow at least...