On Tue 22-09-15 16:49:38, Mel Gorman wrote: [...] > mm: hugetlbfs: Skip shared VMAs when unmapping private pages to satisfy a fault > > SunDong reported the following on https://bugzilla.kernel.org/show_bug.cgi?id=103841 > > I think I find a linux bug, I have the test cases is constructed. I > can stable recurring problems in fedora22(4.0.4) kernel version, > arch for x86_64. I construct transparent huge page, when the parent > and child process with MAP_SHARE, MAP_PRIVATE way to access the same > huge page area, it has the opportunity to lead to huge page copy on > write failure, and then it will munmap the child corresponding mmap > area, but then the child mmap area with VM_MAYSHARE attributes, child > process munmap this area can trigger VM_BUG_ON in set_vma_resv_flags > functions (vma - > vm_flags & VM_MAYSHARE). > > There were a number of problems with the report (e.g. it's hugetlbfs that > triggers this, not transparent huge pages) but it was fundamentally correct > in that a VM_BUG_ON in set_vma_resv_flags() can be triggered that looks > like this > > vma ffff8804651fd0d0 start 00007fc474e00000 end 00007fc475e00000 > next ffff8804651fd018 prev ffff8804651fd188 mm ffff88046b1b1800 > prot 8000000000000027 anon_vma (null) vm_ops ffffffff8182a7a0 > pgoff 0 file ffff88106bdb9800 private_data (null) > flags: 0x84400fb(read|write|shared|mayread|maywrite|mayexec|mayshare|dontexpand|hugetlb) > ------------ > kernel BUG at mm/hugetlb.c:462! > SMP > Modules linked in: xt_pkttype xt_LOG xt_limit iscsi_ibft iscsi_boot_sysfs af_packet ip6t_REJECT nf_reject_ipv6 > xt_tcpudp nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_raw ipt_REJECT nf_reject_ipv4 iptable_raw xt_CT iptable_filter ip6table_mangle > nf_conntrack_netbios_ns nf_conntrack_broadcast nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables xt_conntrack nf_conntrack ip6table_filter > ip6_tables x_tables intel_powerclamp coretemp kvm_intel kvm mgag200 ttm drm_kms_helper drm crct10dif_pclmul crc32_pclmul crc32c_intel > ghash_clmulni_intel aesni_intel aes_x86_64 lrw ipmi_devintf gf128mul iTCO_wdt gpio_ich iTCO_vendor_support glue_helper ablk_helper > dcdbas i7core_edac cryptd syscopyarea sysfillrect bnx2 sysimgblt lpc_ich serio_raw edac_core i2c_algo_bit shpchp mfd_core ipmi_si > tpm_tis tpm ipmi_msghandler wmi acpi_power_meter button acpi_cpufreq processor dm_mod sr_mod cdrom ata_generic hid_generic usbhid hid > uhci_hcd ehci_pci ehci_hcd usbcore ata_piix usb_common megaraid_sas sg > CPU: 38 PID: 26839 Comm: map Not tainted 4.0.4-default #1 > Hardware name: Dell Inc. PowerEdge R810/0TT6JF, BIOS 2.7.4 04/26/2012 > task: ffff88085ed10490 ti: ffff88085ed14000 task.ti: ffff88085ed14000 > set_vma_resv_flags+0x2d/0x30 > > The VM_BUG_ON is correct because private and shared mappings have different > reservation accounting but the warning clearly shows that the VMA is shared. > > When a private COW fails to allocate a new page then only the process that > created the VMA gets the page -- all the children unmap the page. If the > children access that data in the future then they get killed. > > The problem is that the same file is mapped shared and private. During > the COW, the allocation fails, the VMAs are traversed to unmap the other > private pages but a shared VMA is found and the bug is triggered. This > patch identifies such VMAs and skips them. > > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Reported-by: SunDong <sund_sky@xxxxxxx> Reviewed-by: Michal Hocko <mhocko@xxxxxxxx> I guess you wanted to add Cc: stable back. I believe this goes very long way back. > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 999fb0aef8f1..9cc773483624 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -3202,6 +3202,14 @@ static void unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma, > continue; > > /* > + * Shared VMAs have their own reserves and do not affect > + * MAP_PRIVATE accounting but it is possible that a shared > + * VMA is using the same page so check and skip such VMAs. > + */ > + if (iter_vma->vm_flags & VM_MAYSHARE) > + continue; > + > + /* > * Unmap the page from other VMAs without their own reserves. > * They get marked to be SIGKILLed if they fault in these > * areas. This is because a future no-page fault on this VMA -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>