Hi,
I”ve been trying to run btrfs as my primary work filesystem for about 3-4 months now on Fedora 25 systems. I ran a few times into filesystem corruptions. At least one I attributed to a damaged disk, but the last one is with a brand new 3T disk that reports no SMART errors. Worse yet, in at least three cases, the filesystem corruption caused btrfsck to crash. The last filesystem corruption is documented here: https://bugzilla.redhat.com/show_bug.cgi?id=1444821. The dmesg log is in there. The btrfsck crash is here: https://bugzilla.redhat.com/show_bug.cgi?id=1435567. I have two crash modes: either an abort or a SIGSEGV. I checked that both still happens on master as of today. The cause of the abort is that we call set_extent_dirty from check_extent_refs with rec->max_size == 0. I’ve instrumented to try to see where we set this to 0 (see https://github.com/c3d/btrfs-progs/tree/rhbz1435567), and indeed, we do sometimes see max_size set to 0 in a few locations. My instrumentation shows this: 78655 [1.792241:0x451fe0] MAX_SIZE_ZERO: Add extent rec 0x139eb80 max_size 16384 tmpl 0x7fffffffd120 78657 [1.792242:0x451cb8] MAX_SIZE_ZERO: Set max size 0 for rec 0x139ec50 from tmpl 0x7fffffffcf80 78660 [1.792244:0x451fe0] MAX_SIZE_ZERO: Add extent rec 0x139ed50 max_size 16384 tmpl 0x7fffffffd120 I don’t really know what to make of it. The cause of the SIGSEGV is that we try to free a list entry that has its next set to NULL. #0 list_del (entry=0x555555db0420) at /usr/src/debug/btrfs-progs-v4.10.1/kernel-lib/list.h:125 #1 free_all_extent_backrefs (rec=0x555555db0350) at cmds-check.c:5386 #2 maybe_free_extent_rec (extent_cache=0x7fffffffd990, rec=0x555555db0350) at cmds-check.c:5417 #3 0x00005555555b308f in check_block (flags=<optimized out>, buf=0x55557b87cdf0, extent_cache=0x7fffffffd990, root=0x55555587d570) at cmds-check.c:5851 #4 run_next_block (root=root@entry=0x55555587d570, bits=bits@entry=0x5555558841 I don’t know if the two problems are related, but they seem to be pretty consistent on this specific disk, so I think that we have a good opportunity to improve btrfsck to make it more robust to this specific form of corruption. But I don’t want to hapazardly modify a code I don’t really understand. So if anybody could make a suggestion on what the right strategy should be when we have max_size == 0, or how to avoid it in the first place. I don’t know if this is relevant at all, but all the machines that failed that way were used to run VMs with KVM/QEMU. DIsk activity tends to be somewhat intense on occasions, since the VMs running there are part of a personal Jenkins ring that automatically builds various projects. Nominally, there are between three and five guests running (Windows XP, WIndows 10, macOS, Fedora25, Ubuntu 16.04). Thanks Christophe de Dinechin -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
