Switch from using blk_register_region to the probe callback passed to
__register_blkdev to disable the request_module call for an unclaimed
dev_t in the SD majors.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

The swim driver (unlike various other floppy drivers) doesn't have
magic device nodes for certain modes, and already registers a gendisk
for each of the floppies supported by a device.  Thus the region
registered is a no-op and can be removed.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

There is no need to ever register the fake gendisk used for ide-tape.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Add a callback to the major_names array that allows a driver to override
how to probe for dev_t that doesn't currently have a gendisk registered.
This will help separating the lookup of the gendisk by dev_t vs probe
action for a not currently registered dev_t.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Instead of reusing the ranges in bdev_map, add a new helper that is
called if no ranges was found.  This is a first step to unpeel and
eventually remove the complex ranges structure.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Split the block_class_lock mutex into one each to protect bdev_map
and major_names.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Copy and paste the kobj_map functionality in the block code in preparation
for completely rewriting it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Merge three hidden gendisk checks into one.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Just open code it in the few callers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Fold set_device_ro into its only remaining caller.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Use set_disk_ro instead of set_device_ro to match all other block
drivers and to ensure all partitions mirror the read-only flag.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Now that all drivers that want to hook into setting or clearing the
read-only flag use the set_read_only method, this code can be removed.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Implement the ->set_read_only method instead of parsing the actual
ioctl command.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Implement the ->set_read_only method instead of parsing the actual
ioctl command.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Implement the ->set_read_only method instead of parsing the actual
ioctl command.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Add a new method to allow for driver-specific processing when setting or
clearing the block device read-only state.  This allows to replace the
cumbersome and error-prone override of the whole ioctl implementation.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

BLKFLSBUF is entirely contained in the block core, and there is no
good reason to give the driver a hook into processing it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

BLKFLSBUF is not supposed to actually send a flush command to the device,
but to tear down buffer cache structures.  Remove the mtd_blkdevs
implementation and just use the default semantics instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Pull drm fixes from Dave Airlie:
 "Nouveau fixes:

   - atomic modesetting regression fix

   - ttm pre-nv50 fix

   - connector NULL ptr deref fix"

* tag 'drm-fixes-2020-11-16' of git://anongit.freedesktop.org/drm/drm:
  drm/nouveau/kms/nv50-: Use atomic encoder callbacks everywhere
  drm/nouveau/ttm: avoid using nouveau_drm.ttm.type_vram prior to nv50
  drm/nouveau/kms: Fix NULL pointer dereference in nouveau_connector_detect_depth

- atomic modesetting regression fix
- ttm pre-nv50 fix
- connector NULL ptr deref fix
Signed-off-by: Dave Airlie <airlied@redhat.com>
From: Ben Skeggs <skeggsb@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/CACAvsv5D9p78MNN0OxVeRZxN8LDqcadJEGUEFCgWJQ6+_rjPuw@mail.gmail.com

Pull char/misc driver fixes from Greg KH:
 "Here are some small char/misc/whatever driver fixes for 5.10-rc4.

  Nothing huge, lots of small fixes for reported issues:

   - habanalabs driver fixes

   - speakup driver fixes

   - uio driver fixes

   - virtio driver fix

   - other tiny driver fixes

  Full details are in the shortlog.

  All of these have been in linux-next for a full week with no reported
  issues"

* tag 'char-misc-5.10-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
  uio: Fix use-after-free in uio_unregister_device()
  firmware: xilinx: fix out-of-bounds access
  nitro_enclaves: Fixup type and simplify logic of the poll mask setup
  speakup ttyio: Do not schedule() in ttyio_in_nowait
  speakup: Fix clearing selection in safe context
  speakup: Fix var_id_t values and thus keymap
  virtio: virtio_console: fix DMA memory allocation for rproc serial
  habanalabs/gaudi: mask WDT error in QMAN
  habanalabs/gaudi: move coresight mmu config
  habanalabs: fix kernel pointer type
  mei: protect mei_cl_mtu from null dereference

Pull USB and Thunderbolt fixes from Greg KH:
 "Here are some small Thunderbolt and USB driver fixes for 5.10-rc4 to
  solve some reported issues.

  Nothing huge in here, just small things:

   - thunderbolt memory leaks fixed and new device ids added

   - revert of problem patch for the musb driver

   - new quirks added for USB devices

   - typec power supply fixes to resolve much reported problems about
     charging notifications not working anymore

  All except the cdc-acm driver quirk addition have been in linux-next
  with no reported issues (the quirk patch was applied on Friday, and is
  self-contained)"

* tag 'usb-5.10-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb:
  usb: cdc-acm: Add DISABLE_ECHO for Renesas USB Download mode
  MAINTAINERS: add usb raw gadget entry
  usb: typec: ucsi: Report power supply changes
  xhci: hisilicon: fix refercence leak in xhci_histb_probe
  Revert "usb: musb: convert to devm_platform_ioremap_resource_byname"
  thunderbolt: Add support for Intel Tiger Lake-H
  thunderbolt: Only configure USB4 wake for lane 0 adapters
  thunderbolt: Add uaccess dependency to debugfs interface
  thunderbolt: Fix memory leak if ida_simple_get() fails in enumerate_services()
  thunderbolt: Add the missed ida_simple_remove() in ring_request_msix()

Pull kvm fixes from Paolo Bonzini:
 "Fixes for ARM and x86, the latter especially for old processors
  without two-dimensional paging (EPT/NPT)"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  kvm: mmu: fix is_tdp_mmu_check when the TDP MMU is not in use
  KVM: SVM: Update cr3_lm_rsvd_bits for AMD SEV guests
  KVM: x86: Introduce cr3_lm_rsvd_bits in kvm_vcpu_arch
  KVM: x86: clflushopt should be treated as a no-op by emulation
  KVM: arm64: Handle SCXTNUM_ELx traps
  KVM: arm64: Unify trap handlers injecting an UNDEF
  KVM: arm64: Allow setting of ID_AA64PFR0_EL1.CSV2 from userspace

Pull x86 fixes from Thomas Gleixner:
 "A small set of fixes for x86:

   - Cure the fallout from the MSI irqdomain overhaul which missed that
     the Intel IOMMU does not register virtual function devices and
     therefore never reaches the point where the MSI interrupt domain is
     assigned. This made the VF devices use the non-remapped MSI domain
     which is trapped by the IOMMU/remap unit

   - Remove an extra space in the SGI_UV architecture type procfs output
     for UV5

   - Remove a unused function which was missed when removing the UV BAU
     TLB shootdown handler"

* tag 'x86-urgent-2020-11-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  iommu/vt-d: Cure VF irqdomain hickup
  x86/platform/uv: Fix copied UV5 output archtype
  x86/platform/uv: Drop last traces of uv_flush_tlb_others

Pull perf fixes from Thomas Gleixner:
 "A set of fixes for perf:

    - A set of commits which reduce the stack usage of various perf
      event handling functions which allocated large data structs on
      stack causing stack overflows in the worst case

    - Use the proper mechanism for detecting soft interrupts in the
      recursion protection

    - Make the resursion protection simpler and more robust

    - Simplify the scheduling of event groups to make the code more
      robust and prepare for fixing the issues vs. scheduling of
      exclusive event groups

    - Prevent event multiplexing and rotation for exclusive event groups

    - Correct the perf event attribute exclusive semantics to take
      pinned events, e.g. the PMU watchdog, into account

    - Make the anythread filtering conditional for Intel's generic PMU
      counters as it is not longer guaranteed to be supported on newer
      CPUs. Check the corresponding CPUID leaf to make sure

    - Fixup a duplicate initialization in an array which was probably
      caused by the usual 'copy & paste - forgot to edit' mishap"

* tag 'perf-urgent-2020-11-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/intel/uncore: Fix Add BW copypasta
  perf/x86/intel: Make anythread filter support conditional
  perf: Tweak perf_event_attr::exclusive semantics
  perf: Fix event multiplexing for exclusive groups
  perf: Simplify group_sched_in()
  perf: Simplify group_sched_out()
  perf/x86: Make dummy_iregs static
  perf/arch: Remove perf_sample_data::regs_user_copy
  perf: Optimize get_recursion_context()
  perf: Fix get_recursion_context()
  perf/x86: Reduce stack usage for x86_pmu::drain_pebs()
  perf: Reduce stack usage of perf_output_begin()

Pull scheduler fixes from Thomas Gleixner:
 "A set of scheduler fixes:

   - Address a load balancer regression by making the load balancer use
     the same logic as the wakeup path to spread tasks in the LLC domain

   - Prefer the CPU on which a task run last over the local CPU in the
     fast wakeup path for asymmetric CPU capacity systems to align with
     the symmetric case. This ensures more locality and prevents massive
     migration overhead on those asymetric systems

   - Fix a memory corruption bug in the scheduler debug code caused by
     handing a modified buffer pointer to kfree()"

* tag 'sched-urgent-2020-11-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/debug: Fix memory corruption caused by multiple small reads of flags
  sched/fair: Prefer prev cpu in asymmetric wakeup path
  sched/fair: Ensure tasks spreading in LLC during LB

Pull locking fixes from Thomas Gleixner:
 "Two fixes for the locking subsystem:

   - Prevent an unconditional interrupt enable in a futex helper
     function which can be called from contexts which expect interrupts
     to stay disabled across the call

   - Don't modify lockdep chain keys in the validation process as that
     causes chain inconsistency"

* tag 'locking-urgent-2020-11-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  lockdep: Avoid to modify chain keys in validate_chain()
  futex: Don't enable IRQs unconditionally in put_pi_state()

Pull percpu fix and cleanup from Dennis Zhou:
 "A fix for a Wshadow warning in the asm-generic percpu macros came in
  and then I tacked on the removal of flexible array initializers in the
  percpu allocator"

* 'for-5.10-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu:
  percpu: convert flexible array initializers to use struct_size()
  asm-generic: percpu: avoid Wshadow warning

In some cases where shadow paging is in use, the root page will
be either mmu->pae_root or vcpu->arch.mmu->lm_root.  Then it will
not have an associated struct kvm_mmu_page, because it is allocated
with alloc_page instead of kvm_mmu_alloc_page.

Just return false quickly from is_tdp_mmu_root if the TDP MMU is
not in use, which also includes the case where shadow paging is
enabled.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Merge fixes from Andrew Morton:
 "14 patches.

  Subsystems affected by this patch series: mm (migration, vmscan, slub,
  gup, memcg, hugetlbfs), mailmap, kbuild, reboot, watchdog, panic, and
  ocfs2"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  ocfs2: initialize ip_next_orphan
  panic: don't dump stack twice on warn
  hugetlbfs: fix anon huge page migration race
  mm: memcontrol: fix missing wakeup polling thread
  kernel/watchdog: fix watchdog_allowed_mask not used warning
  reboot: fix overflow parsing reboot cpu number
  Revert "kernel/reboot.c: convert simple_strtoul to kstrtoint"
  compiler.h: fix barrier_data() on clang
  mm/gup: use unpin_user_pages() in __gup_longterm_locked()
  mm/slub: fix panic in slab_alloc_node()
  mailmap: fix entry for Dmitry Baryshkov/Eremin-Solenikov
  mm/vmscan: fix NR_ISOLATED_FILE corruption on 64-bit
  mm/compaction: stop isolation if too many pages are isolated and we have pages to migrate
  mm/compaction: count pages and stop correctly during page isolation

Pull clk fixes from Stephen Boyd:
 "Two small clk driver fixes:

   - Make to_clk_regmap() inline to avoid compiler annoyance

   - Fix critical clks on i.MX imx8m SoCs"

* tag 'clk-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux:
  clk: imx8m: fix bus critical clk registration
  clk: define to_clk_regmap() as inline function

Merge tag 'hwmon-for-v5.10-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging

Pull hwmon fixes from Guenter Roeck:

 - Fix potential bufer overflow in pmbus/max20730 driver

 - Fix locking issue in pmbus core

 - Fix regression causing timeouts in applesmc driver

 - Fix RPM calculation in pwm-fan driver

 - Restrict counter visibility in amd_energy driver

* tag 'hwmon-for-v5.10-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging:
  hwmon: (amd_energy) modify the visibility of the counters
  hwmon: (applesmc) Re-work SMC comms
  hwmon: (pwm-fan) Fix RPM calculation
  hwmon: (pmbus) Add mutex locking for sysfs reads
  hwmon: (pmbus/max20730) use scnprintf() instead of snprintf()

Pull SCSI fixes from James Bottomley:
 "Three small fixes, all in the embedded ufs driver subsystem"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  scsi: ufshcd: Fix missing destroy_workqueue()
  scsi: ufs: Try to save power mode change and UIC cmd completion timeout
  scsi: ufs: Fix unbalanced scsi_block_reqs_cnt caused by ufshcd_hold()

Pull selinux fix from Paul Moore:
 "One small SELinux patch to make sure we return an error code when an
  allocation fails. It passes all of our tests, but given the nature of
  the patch that isn't surprising"

* tag 'selinux-pr-20201113' of git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux:
  selinux: Fix error return code in sel_ib_pkey_sid_slow()

Pull uml fix from Richard Weinberger:
 "Call PMD destructor in __pmd_free_tlb()"

* tag 'for-linus-5.10-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml:
  um: Call pgtable_pmd_page_dtor() in __pmd_free_tlb()

When afs_write_end() is called with copied == 0, it tries to set the
dirty region, but there's no way to actually encode a 0-length region in
the encoding in page->private.

"0,0", for example, indicates a 1-byte region at offset 0.  The maths
miscalculates this and sets it incorrectly.

Fix it to just do nothing but unlock and put the page in this case.  We
don't actually need to mark the page dirty as nothing presumably
changed.

Fixes: 65dd2d60 ("afs: Alter dirty range encoding in page->private")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Though problem if found on a lower 4.1.12 kernel, I think upstream has
same issue.

In one node in the cluster, there is the following callback trace:

   # cat /proc/21473/stack
   __ocfs2_cluster_lock.isra.36+0x336/0x9e0 [ocfs2]
   ocfs2_inode_lock_full_nested+0x121/0x520 [ocfs2]
   ocfs2_evict_inode+0x152/0x820 [ocfs2]
   evict+0xae/0x1a0
   iput+0x1c6/0x230
   ocfs2_orphan_filldir+0x5d/0x100 [ocfs2]
   ocfs2_dir_foreach_blk+0x490/0x4f0 [ocfs2]
   ocfs2_dir_foreach+0x29/0x30 [ocfs2]
   ocfs2_recover_orphans+0x1b6/0x9a0 [ocfs2]
   ocfs2_complete_recovery+0x1de/0x5c0 [ocfs2]
   process_one_work+0x169/0x4a0
   worker_thread+0x5b/0x560
   kthread+0xcb/0xf0
   ret_from_fork+0x61/0x90

The above stack is not reasonable, the final iput shouldn't happen in
ocfs2_orphan_filldir() function.  Looking at the code,

  2067         /* Skip inodes which are already added to recover list, since dio may
  2068          * happen concurrently with unlink/rename */
  2069         if (OCFS2_I(iter)->ip_next_orphan) {
  2070                 iput(iter);
  2071                 return 0;
  2072         }
  2073

The logic thinks the inode is already in recover list on seeing
ip_next_orphan is non-NULL, so it skip this inode after dropping a
reference which incremented in ocfs2_iget().

While, if the inode is already in recover list, it should have another
reference and the iput() at line 2070 should not be the final iput
(dropping the last reference).  So I don't think the inode is really in
the recover list (no vmcore to confirm).

Note that ocfs2_queue_orphans(), though not shown up in the call back
trace, is holding cluster lock on the orphan directory when looking up
for unlinked inodes.  The on disk inode eviction could involve a lot of
IOs which may need long time to finish.  That means this node could hold
the cluster lock for very long time, that can lead to the lock requests
(from other nodes) to the orhpan directory hang for long time.

Looking at more on ip_next_orphan, I found it's not initialized when
allocating a new ocfs2_inode_info structure.

This causes te reflink operations from some nodes hang for very long
time waiting for the cluster lock on the orphan directory.

Fix: initialize ip_next_orphan as NULL.
Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201109171746.27884-1-wen.gang.wang@oracle.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Before commit 3f388f28 ("panic: dump registers on panic_on_warn"),
__warn() was calling show_regs() when regs was not NULL, and show_stack()
otherwise.

After that commit, show_stack() is called regardless of whether
show_regs() has been called or not, leading to duplicated Call Trace:

  ------------[ cut here ]------------
  WARNING: CPU: 0 PID: 1 at arch/powerpc/mm/nohash/8xx.c:186 mmu_mark_initmem_nx+0x24/0x94
  CPU: 0 PID: 1 Comm: swapper Not tainted 5.10.0-rc2-s3k-dev-01375-gf46ec0d3ecbd-dirty #4092
  NIP:  c00128b4 LR: c0010228 CTR: 00000000
  REGS: c9023e40 TRAP: 0700   Not tainted  (5.10.0-rc2-s3k-dev-01375-gf46ec0d3ecbd-dirty)
  MSR:  00029032 <EE,ME,IR,DR,RI>  CR: 24000424  XER: 00000000

  GPR00: c0010228 c9023ef8 c2100000 0074c000 ffffffff 00000000 c2151000 c07b3880
  GPR08: ff000900 0074c000 c8000000 c33b53a8 24000822 00000000 c0003a20 00000000
  GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
  GPR24: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00800000
  NIP [c00128b4] mmu_mark_initmem_nx+0x24/0x94
  LR [c0010228] free_initmem+0x20/0x58
  Call Trace:
    free_initmem+0x20/0x58
    kernel_init+0x1c/0x114
    ret_from_kernel_thread+0x14/0x1c
  Instruction dump:
  7d291850 7d234b78 4e800020 9421ffe0 7c0802a6 bfc10018 3fe0c060 3bff0000
  3fff4080 3bffffff 90010024 57ff0010 <0fe00000> 392001cd 7c3e0b78 953e0008
  CPU: 0 PID: 1 Comm: swapper Not tainted 5.10.0-rc2-s3k-dev-01375-gf46ec0d3ecbd-dirty #4092
  Call Trace:
    __warn+0x8c/0xd8 (unreliable)
    report_bug+0x11c/0x154
    program_check_exception+0x1dc/0x6e0
    ret_from_except_full+0x0/0x4
  --- interrupt: 700 at mmu_mark_initmem_nx+0x24/0x94
      LR = free_initmem+0x20/0x58
    free_initmem+0x20/0x58
    kernel_init+0x1c/0x114
    ret_from_kernel_thread+0x14/0x1c
  ---[ end trace 31702cd2a9570752 ]---

Only call show_stack() when regs is NULL.

Fixes: 3f388f28 ("panic: dump registers on panic_on_warn")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lkml.kernel.org/r/e8c055458b080707f1bc1a98ff8bea79d0cec445.1604748361.git.christophe.leroy@csgroup.euSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Qian Cai reported the following BUG in [1]

  LTP: starting move_pages12
  BUG: unable to handle page fault for address: ffffffffffffffe0
  ...
  RIP: 0010:anon_vma_interval_tree_iter_first+0xa2/0x170 avc_start_pgoff at mm/interval_tree.c:63
  Call Trace:
    rmap_walk_anon+0x141/0xa30 rmap_walk_anon at mm/rmap.c:1864
    try_to_unmap+0x209/0x2d0 try_to_unmap at mm/rmap.c:1763
    migrate_pages+0x1005/0x1fb0
    move_pages_and_store_status.isra.47+0xd7/0x1a0
    __x64_sys_move_pages+0xa5c/0x1100
    do_syscall_64+0x5f/0x310
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

Hugh Dickins diagnosed this as a migration bug caused by code introduced
to use i_mmap_rwsem for pmd sharing synchronization.  Specifically, the
routine unmap_and_move_huge_page() is always passing the TTU_RMAP_LOCKED
flag to try_to_unmap() while holding i_mmap_rwsem.  This is wrong for
anon pages as the anon_vma_lock should be held in this case.  Further
analysis suggested that i_mmap_rwsem was not required to he held at all
when calling try_to_unmap for anon pages as an anon page could never be
part of a shared pmd mapping.

Discussion also revealed that the hack in hugetlb_page_mapping_lock_write
to drop page lock and acquire i_mmap_rwsem is wrong.  There is no way to
keep mapping valid while dropping page lock.

This patch does the following:

 - Do not take i_mmap_rwsem and set TTU_RMAP_LOCKED for anon pages when
   calling try_to_unmap.

 - Remove the hacky code in hugetlb_page_mapping_lock_write. The routine
   will now simply do a 'trylock' while still holding the page lock. If
   the trylock fails, it will return NULL. This could impact the
   callers:

    - migration calling code will receive -EAGAIN and retry up to the
      hard coded limit (10).

    - memory error code will treat the page as BUSY. This will force
      killing (SIGKILL) instead of SIGBUS any mapping tasks.

   Do note that this change in behavior only happens when there is a
   race. None of the standard kernel testing suites actually hit this
   race, but it is possible.

[1] https://lore.kernel.org/lkml/20200708012044.GC992@lca.pw/
[2] https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2010071833100.2214@eggly.anvils/

Fixes: c0d0381a ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization")
Reported-by: Qian Cai <cai@lca.pw>
Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201105195058.78401-1-mike.kravetz@oracle.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>