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linux/arch/sparc/kernel
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Nicholas Piggin bafb056ce2 sparc64: remove mm_cpumask clearing to fix kthread_use_mm race 
The de facto (and apparently uncommented) standard for using an mm had,
thanks to this code in sparc if nothing else, been that you must have a
reference on mm_users *and that reference must have been obtained with
mmget()*, i.e., from a thread with a reference to mm_users that had used
the mm.

The introduction of mmget_not_zero() in commit d2005e3f41
("userfaultfd: don't pin the user memory in userfaultfd_file_create()")
allowed mm_count holders to aoperate on user mappings asynchronously
from the actual threads using the mm, but they were not to load those
mappings into their TLB (i.e., walking vmas and page tables is okay,
kthread_use_mm() is not).

io_uring 2b188cc1bb ("Add io_uring IO interface") added code which
does a kthread_use_mm() from a mmget_not_zero() refcount.

The problem with this is code which previously assumed mm == current->mm
and mm->mm_users == 1 implies the mm will remain single-threaded at
least until this thread creates another mm_users reference, has now
broken.

arch/sparc/kernel/smp_64.c:

    if (atomic_read(&mm->mm_users) == 1) {
        cpumask_copy(mm_cpumask(mm), cpumask_of(cpu));
        goto local_flush_and_out;
    }

vs fs/io_uring.c

    if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL) ||
                 !mmget_not_zero(ctx->sqo_mm)))
        return -EFAULT;
    kthread_use_mm(ctx->sqo_mm);

mmget_not_zero() could come in right after the mm_users == 1 test, then
kthread_use_mm() which sets its CPU in the mm_cpumask. That update could
be lost if cpumask_copy() occurs afterward.

I propose we fix this by allowing mmget_not_zero() to be a first-class
reference, and not have this obscure undocumented and unchecked
restriction.

The basic fix for sparc64 is to remove its mm_cpumask clearing code. The
optimisation could be effectively restored by sending IPIs to mm_cpumask
members and having them remove themselves from mm_cpumask. This is more
tricky so I leave it as an exercise for someone with a sparc64 SMP.
powerpc has a (currently similarly broken) example.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200914045219.3736466-4-npiggin@gmail.com
2020-09-16 12:24:37 +10:00
..
syscalls all arch: remove system call sys_sysctl 2020-08-14 19:56:56 -07:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
adi_64.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 482 2019-06-19 17:09:52 +02:00
apc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
asm-offsets.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
audit.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
auxio_32.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
auxio_64.c sparc: Use of_node_name_eq for node name comparisons 2018-11-18 13:35:21 -08:00
btext.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
central.c sparc: Use of_node_name_eq for node name comparisons 2018-11-18 13:35:21 -08:00
cherrs.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
chmc.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
compat_audit.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cpu.c mm: reorder includes after introduction of linux/pgtable.h 2020-06-09 09:39:13 -07:00
cpumap.c sparc64: Replace zero-length array with flexible-array 2020-05-07 18:49:04 -07:00
cpumap.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
devices.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ds.c sparc64: Replace zero-length array with flexible-array 2020-05-07 18:49:04 -07:00
dtlb_miss.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
dtlb_prot.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ebus.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
entry.h sparc64: Add support for ADI register fields, ASIs and traps 2018-03-18 07:38:45 -07:00
entry.S sparc: share process creation helpers between sparc and sparc64 2020-06-23 10:49:56 +02:00
etrap_32.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
etrap_64.S sparc64: Add support for ADI (Application Data Integrity) 2018-03-18 07:38:48 -07:00
fpu_traps.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ftrace.c sparc/function_graph: Simplify with function_graph_enter() 2018-11-27 20:31:46 -05:00
getsetcc.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
head_32.S sparc32: mm: Restructure sparc32 MMU page-table layout 2020-05-13 15:32:00 -07:00
head_64.S mm: reorder includes after introduction of linux/pgtable.h 2020-06-09 09:39:13 -07:00
helpers.S treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
hvapi.c sparc64: Oracle DAX infrastructure 2018-01-22 08:17:15 -08:00
hvcalls.S sparc64: Oracle DAX infrastructure 2018-01-22 08:17:15 -08:00
hvtramp.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
idprom.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
iommu_common.h sparc: remove the mapping_error dma_map_ops method 2018-12-06 06:56:40 -08:00
iommu-common.c iommu-common: move to arch/sparc 2018-05-09 06:54:27 +02:00
iommu.c sparc64/iommu: allow large DMA masks 2019-02-20 07:28:58 -07:00
ioport.c sparc32: use per-device dma_ops 2020-04-02 18:11:55 -07:00
irq_32.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
irq_64.c sparc: Use of_node_name_eq for node name comparisons 2018-11-18 13:35:21 -08:00
irq.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
itlb_miss.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ivec.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
jump_label.c jump_label: move 'asm goto' support test to Kconfig 2019-01-06 09:46:51 +09:00
kernel.h sparc: share process creation helpers between sparc and sparc64 2020-06-23 10:49:56 +02:00
kgdb_32.c kgdb/treewide: constify struct kgdb_arch arch_kgdb_ops 2018-12-30 08:33:06 +00:00
kgdb_64.c kgdb/treewide: constify struct kgdb_arch arch_kgdb_ops 2018-12-30 08:33:06 +00:00
kprobes.c bpf/error-inject/kprobes: Clear current_kprobe and enable preempt in kprobe 2018-06-21 12:33:19 +02:00
kstack.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ktlb.S mm: reorder includes after introduction of linux/pgtable.h 2020-06-09 09:39:13 -07:00
ldc.c iommu-common: move to arch/sparc 2018-05-09 06:54:27 +02:00
led.c proc: convert everything to "struct proc_ops" 2020-02-04 03:05:26 +00:00
leon_kernel.c sparc: Remove unused leon_trans_init 2018-11-18 13:35:22 -08:00
leon_pci_grpci1.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
leon_pci_grpci2.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
leon_pci.c sparc/PCI: Use dev_printk() when possible 2018-05-22 07:54:06 -05:00
leon_pmc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
leon_smp.c mm: remove unneeded includes of <asm/pgalloc.h> 2020-08-07 11:33:26 -07:00
Makefile sparc: share process creation helpers between sparc and sparc64 2020-06-23 10:49:56 +02:00
mdesc.c mdesc: fix a missing-check bug in get_vdev_port_node_info() 2019-06-02 22:15:35 -07:00
misctrap.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
module.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
nmi.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
of_device_32.c sparc: Use DT node full_name instead of name for resources 2018-11-18 13:35:22 -08:00
of_device_64.c sparc: Use DT node full_name instead of name for resources 2018-11-18 13:35:22 -08:00
of_device_common.c sparc32: use per-device dma_ops 2020-04-02 18:11:55 -07:00
of_device_common.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci_common.c sparc/PCI: Use dev_printk() when possible 2018-05-22 07:54:06 -05:00
pci_fire.c mm: replace all open encodings for NUMA_NO_NODE 2019-03-05 21:07:14 -08:00
pci_impl.h sparc/PCI: Support arbitrary host bridge address offset 2018-02-15 15:07:30 -06:00
pci_msi.c sparc/PCI: Use dev_printk() when possible 2018-05-22 07:54:06 -05:00
pci_psycho.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci_sabre.c sparc: Use of_node_name_eq for node name comparisons 2018-11-18 13:35:21 -08:00
pci_schizo.c mm: replace all open encodings for NUMA_NO_NODE 2019-03-05 21:07:14 -08:00
pci_sun4v_asm.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci_sun4v.c sparc64/pci_sun4v: fix ATU checks for large DMA masks 2019-04-10 21:42:04 +02:00
pci_sun4v.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
pci.c mm: reorder includes after introduction of linux/pgtable.h 2020-06-09 09:39:13 -07:00
pcic.c sparc/PCI: Use dev_printk() when possible 2018-05-22 07:54:06 -05:00
pcr.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
perf_event.c sparc: perf: fix updated event period in response to PERF_EVENT_IOC_PERIOD 2019-06-02 22:16:33 -07:00
pmc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
power.c sparc: Convert to using %pOFn instead of device_node.name 2018-11-18 13:35:20 -08:00
process_32.c Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-09 13:33:54 -07:00
process_64.c Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-09 13:33:54 -07:00
process.c arch: rename copy_thread_tls() back to copy_thread() 2020-07-04 23:41:37 +02:00
prom_32.c sparc32, leon: Stop adding vendor and device id to prom ambapp path components 2020-01-21 13:24:35 +01:00
prom_64.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
prom_common.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
prom_irqtrans.c sparc: Use device_type helpers to access the node type 2018-11-18 13:35:21 -08:00
prom.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
psycho_common.c mm: replace all open encodings for NUMA_NO_NODE 2019-03-05 21:07:14 -08:00
psycho_common.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ptrace_32.c sparc: switch to ->regset_get() 2020-07-27 14:31:08 -04:00
ptrace_64.c sparc: switch to ->regset_get() 2020-07-27 14:31:08 -04:00
reboot.c sparc: Use device_type helpers to access the node type 2018-11-18 13:35:21 -08:00
rtrap_32.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
rtrap_64.S sched/rt, sparc: Use CONFIG_PREEMPTION 2019-12-08 14:37:35 +01:00
sbus.c mm: replace all open encodings for NUMA_NO_NODE 2019-03-05 21:07:14 -08:00
setup_32.c initrd: remove support for multiple floppies 2020-07-30 08:22:33 +02:00
setup_64.c initrd: remove support for multiple floppies 2020-07-30 08:22:33 +02:00
signal32.c mm: don't include asm/pgtable.h if linux/mm.h is already included 2020-06-09 09:39:13 -07:00
signal_32.c mm: remove unneeded includes of <asm/pgalloc.h> 2020-08-07 11:33:26 -07:00
signal_64.c mm: don't include asm/pgtable.h if linux/mm.h is already included 2020-06-09 09:39:13 -07:00
sigutil_32.c Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
sigutil_64.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sigutil.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
smp_32.c mm: remove unneeded includes of <asm/pgalloc.h> 2020-08-07 11:33:26 -07:00
smp_64.c sparc64: remove mm_cpumask clearing to fix kthread_use_mm race 2020-09-16 12:24:37 +10:00
sparc_ksyms.c sparc: move exports to definitions 2016-08-07 23:55:43 -04:00
spiterrs.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sstate.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
stacktrace.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
starfire.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sun4d_irq.c sparc: Use of_node_name_eq for node name comparisons 2018-11-18 13:35:21 -08:00
sun4d_smp.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sun4m_irq.c mm: remove unneeded includes of <asm/pgalloc.h> 2020-08-07 11:33:26 -07:00
sun4m_smp.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sun4v_ivec.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sun4v_mcd.S treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 482 2019-06-19 17:09:52 +02:00
sun4v_tlb_miss.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
sys32.S net: remove compat_sys_{get,set}sockopt 2020-07-19 18:16:40 -07:00
sys_sparc32.c sparc: remove unused header file nfs_fs.h 2020-06-02 18:41:48 -07:00
sys_sparc_32.c signal: Remove the task parameter from force_sig_fault 2019-05-29 09:31:43 -05:00
sys_sparc_64.c sparc64: fix adjtimex regression 2020-02-02 11:54:41 +01:00
syscalls.S sparc64: enable HAVE_COPY_THREAD_TLS 2020-06-23 10:49:54 +02:00
sysfs.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
systbls_32.S sparc: generate uapi header and system call table files 2018-11-18 18:52:22 -08:00
systbls_64.S sparc: generate uapi header and system call table files 2018-11-18 18:52:22 -08:00
systbls.h sparc: get rid of asm wrapper for nis_syscall() 2018-03-20 12:05:17 -04:00
time_32.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
time_64.c cpufreq: Call transition notifier only once for each policy 2019-05-10 12:20:36 +02:00
trampoline_32.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
trampoline_64.S mm: reorder includes after introduction of linux/pgtable.h 2020-06-09 09:39:13 -07:00
traps_32.c mm: reorder includes after introduction of linux/pgtable.h 2020-06-09 09:39:13 -07:00
traps_64.c mm: don't include asm/pgtable.h if linux/mm.h is already included 2020-06-09 09:39:13 -07:00
tsb.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ttable_32.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ttable_64.S sparc64: Add support for ADI register fields, ASIs and traps 2018-03-18 07:38:45 -07:00
una_asm_32.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
una_asm_64.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
unaligned_32.c Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
unaligned_64.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
uprobes.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 13 2019-05-21 11:28:45 +02:00
urtt_fill.S sparc64: Add support for ADI (Application Data Integrity) 2018-03-18 07:38:48 -07:00
utrap.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vdso.c locking/seqlock, headers: Untangle the spaghetti monster 2020-08-06 16:13:13 +02:00
vio.c sparc: use scnprintf() in show_pciobppath_attr() in vio.c 2020-05-13 15:35:58 -07:00
viohs.c sparc64: viohs: Remove VLA usage 2018-10-07 22:42:00 -07:00
visemul.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vmlinux.lds.S Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc 2020-01-30 07:36:43 -08:00
windows.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
winfixup.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
wof.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
wuf.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00