When running several builders in parallel, on QEMU, with 8GB of memory, a fatal kernel trap caused by llan driver is sometimes observed, when the system starts to run out of swap space. fatal kernel trap: exception = 0x300 (data storage interrupt) virtual address = 0x18 dsisr = 0x42000000 srr0 = 0xc000000000ac9104 (0xac9104) srr1 = 0x8000000000009032 current msr = 0x8000000000009032 lr = 0xc000000000ac90ec (0xac90ec) curthread = 0xc000000006deb000 pid = 12, comm = irq16781321: llan0 panic: data storage interrupt trap cpuid = 2 time = 1549288422 KDB: stack backtrace: 0xe0000000005a5ed0: at .kdb_backtrace+0x5c 0xe0000000005a6000: at .vpanic+0x1b4 0xe0000000005a60c0: at .panic+0x38 0xe0000000005a6150: at .trap_fatal+0x25c 0xe0000000005a61e0: at .trap+0xeec 0xe0000000005a6380: at .powerpc_interrupt+0x290 0xe0000000005a6420: kernel DSI write trap @ 0x18 by .llan_intr+0xf4: srr1=0x8000000000009032 r1=0xe0000000005a66d0 cr=0x22000042 xer=0 ctr=0 r2=0xc000000001569528 sr=0x42000000 0xe0000000005a66d0: at .llan_intr+0xd8 0xe0000000005a6770: at .ithread_loop+0x25c 0xe0000000005a6850: at .fork_exit+0xd0 0xe0000000005a68f0: at .fork_trampoline+0x10 0xe0000000005a6920: at -0x4 KDB: enter: panic [ thread pid 12 tid 100153 ] Stopped at .kdb_enter+0x60: ld r2, r1, 0x28 db> It seems like there is some point in the driver that does not check properly if UMA allocation failed.
A commit references this bug: Author: luporl Date: Tue Feb 5 18:16:14 UTC 2019 New revision: 343791 URL: https://svnweb.freebsd.org/changeset/base/343791 Log: [ppc64] llan: fix fatal kernel trap when system is low on memory When running several builders in parallel, on QEMU, with 8GB of memory, a fatal kernel trap (0x300 (data storage interrupt)) caused by llan driver is sometimes observed, when the system starts to run out of swap space. This happens because, at llan_intr(), a phyp call to add a logical LAN buffer is always made when llan_add_rxbuf() fails, even if it fails to allocate a new buffer. PR: 235489 Reviewed by: jhibbits Differential Revision: https://reviews.freebsd.org/D19084 Changes: head/sys/powerpc/pseries/phyp_llan.c