The new riscv specific arch_hugetlb_migration_supported() must be
guarded with a #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION to avoid
the following build error:

In file included from include/linux/hugetlb.h:851,
                    from kernel/fork.c:52:
>> arch/riscv/include/asm/hugetlb.h:15:42: error: static declaration of 'arch_hugetlb_migration_supported' follows non-static declaration
      15 | #define arch_hugetlb_migration_supported arch_hugetlb_migration_supported
         |                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/hugetlb.h:916:20: note: in expansion of macro 'arch_hugetlb_migration_supported'
     916 | static inline bool arch_hugetlb_migration_supported(struct hstate *h)
         |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   arch/riscv/include/asm/hugetlb.h:14:6: note: previous declaration of 'arch_hugetlb_migration_supported' with type 'bool(struct hstate *)' {aka '_Bool(struct hstate *)'}
      14 | bool arch_hugetlb_migration_supported(struct hstate *h);
         |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202402110258.CV51JlEI-lkp@intel.com/
Fixes: ce68c035 ("riscv: Fix arch_hugetlb_migration_supported() for NAPOT")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240211083640.756583-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Previous commit dbfbda3b ("riscv: mm: update T-Head memory type
definitions") from patch [1] missed a `<` for bit shifting, result in
bit(61) does not set in _PAGE_NOCACHE_THEAD and leaves bit(0) set instead.
This patch get this fixed.

Link: https://lore.kernel.org/linux-riscv/20230912072510.2510-1-jszhang@kernel.org/ [1]
Fixes: dbfbda3b ("riscv: mm: update T-Head memory type definitions")
Signed-off-by: Yangyu Chen <cyy@cyyself.name>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/tencent_E19FA1A095768063102E654C6FC858A32F06@qq.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

CALLER_ADDRx returns caller's address at specified level, they are used
for several tracers. These macros eventually use
__builtin_return_address(n) to get the caller's address if arch doesn't
define their own implementation.

In RISC-V, __builtin_return_address(n) only works when n == 0, we need
to walk the stack frame to get the caller's address at specified level.

data.level started from 'level + 3' due to the call flow of getting
caller's address in RISC-V implementation. If we don't have additional
three iteration, the level is corresponding to follows:

callsite -> return_address -> arch_stack_walk -> walk_stackframe
|           |                 |                  |
level 3     level 2           level 1            level 0

Fixes: 10626c32 ("riscv/ftrace: Add basic support")
Cc: stable@vger.kernel.org
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Zong Li <zong.li@sifive.com>
Link: https://lore.kernel.org/r/20240202015102.26251-1-zong.li@sifive.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

This single fix is also part of a larger cleanup, so I'm merging it
into my fixes branch so it can be shared with for-next.

* commit '8246601a':
  riscv: tlb: fix __p*d_free_tlb()

Nathan Chancellor <nathan@kernel.org> says:

Eric reported that builds of LLVM with [1] (close to tip of tree) have
CONFIG_AS_HAS_OPTION_ARCH=n because the test for expected failure on
invalid input has started succeeding.

This Kconfig test was added because '.option arch' only causes an
assembler warning when it is unsupported, rather than a hard error,
which is what users of as-instr expect when something is unsupported.

This can be resolved by turning assembler warnings into errors with
'-Wa,--fatal-warnings' like we do with the compiler with '-Werror',
which is what the first patch does. The second patch removes the invalid
test, as the valid test is good enough with fatal warnings.

I have diffed several configurations for the different architectures
that use as-instr and I have found no issues.

[1]: https://github.com/llvm/llvm-project/commit/3ac9fe69f70a2b3541266daedbaaa7dc9c007a2a

* b4-shazam-merge:
  RISC-V: Drop invalid test from CONFIG_AS_HAS_OPTION_ARCH
  kbuild: Add -Wa,--fatal-warnings to as-instr invocation

Link: https://lore.kernel.org/r/20240125-fix-riscv-option-arch-llvm-18-v1-0-390ac9cc3cd0@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Commit e4bb020f ("riscv: detect assembler support for .option arch")
added two tests, one for a valid value to '.option arch' that should
succeed and one for an invalid value that is expected to fail to make
sure that support for '.option arch' is properly detected because Clang
does not error when '.option arch' is not supported:

  $ clang --target=riscv64-linux-gnu -Werror -x assembler -c -o /dev/null <(echo '.option arch, +m')
  /dev/fd/63:1:9: warning: unknown option, expected 'push', 'pop', 'rvc', 'norvc', 'relax' or 'norelax'
  .option arch, +m
          ^
  $ echo $?
  0

Unfortunately, the invalid test started being accepted by Clang after
the linked llvm-project change, which causes CONFIG_AS_HAS_OPTION_ARCH
and configurations that depend on it to be silently disabled, even
though those versions do support '.option arch'.

The invalid test can be avoided altogether by using
'-Wa,--fatal-warnings', which will turn all assembler warnings into
errors, like '-Werror' does for the compiler:

  $ clang --target=riscv64-linux-gnu -Werror -Wa,--fatal-warnings -x assembler -c -o /dev/null <(echo '.option arch, +m')
  /dev/fd/63:1:9: error: unknown option, expected 'push', 'pop', 'rvc', 'norvc', 'relax' or 'norelax'
  .option arch, +m
          ^
  $ echo $?
  1

The as-instr macros have been updated to make use of this flag, so
remove the invalid test, which allows CONFIG_AS_HAS_OPTION_ARCH to work
for all compiler versions.

Cc: stable@vger.kernel.org
Fixes: e4bb020f ("riscv: detect assembler support for .option arch")
Link: https://github.com/llvm/llvm-project/commit/3ac9fe69f70a2b3541266daedbaaa7dc9c007a2aReported-by: Eric Biggers <ebiggers@kernel.org>
Closes: https://lore.kernel.org/r/20240121011341.GA97368@sol.localdomain/Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Eric Biggers <ebiggers@google.com>
Tested-by: Andy Chiu <andybnac@gmail.com>
Reviewed-by: Andy Chiu <andybnac@gmail.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20240125-fix-riscv-option-arch-llvm-18-v1-2-390ac9cc3cd0@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Certain assembler instruction tests may only induce warnings from the
assembler on an unsupported instruction or option, which causes as-instr
to succeed when it was expected to fail. Some tests workaround this
limitation by additionally testing that invalid input fails as expected.
However, this is fragile if the assembler is changed to accept the
invalid input, as it will cause the instruction/option to be unavailable
like it was unsupported even when it is.

Use '-Wa,--fatal-warnings' in the as-instr macro to turn these warnings
into hard errors, which avoids this fragility and makes tests more
robust and well formed.

Cc: stable@vger.kernel.org
Suggested-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Eric Biggers <ebiggers@google.com>
Tested-by: Andy Chiu <andybnac@gmail.com>
Reviewed-by: Andy Chiu <andybnac@gmail.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20240125-fix-riscv-option-arch-llvm-18-v1-1-390ac9cc3cd0@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

We must clear the cpumask once we have flushed the batch, otherwise cpus
get accumulated and we end sending IPIs to more cpus than needed.

Fixes: 54d7431a ("riscv: Add support for BATCHED_UNMAP_TLB_FLUSH")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20240130115508.105386-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

The percpu area overflow_stacks is exported from arch/riscv/kernel/traps.c
for use in the entry code, but is not declared anywhere. Add the relevant
declaration to arch/riscv/include/asm/stacktrace.h to silence the following
sparse warning:

arch/riscv/kernel/traps.c:395:1: warning: symbol '__pcpu_scope_overflow_stack' was not declared. Should it be static?

We don't add the stackinfo_get_overflow() call as for some of the other
architectures as this doesn't seem to be used yet, so just silence the
warning.
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Fixes: be97d0db ("riscv: VMAP_STACK overflow detection thread-safe")
Link: https://lore.kernel.org/r/20231123134214.81481-1-ben.dooks@codethink.co.ukSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch_hugetlb_migration_supported() must be reimplemented to add support
for NAPOT hugepages, which is done here.

Fixes: 82a1a1f3 ("riscv: mm: support Svnapot in hugetlb page")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240130120114.106003-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

The riscv privileged specification mandates to flush the TLB whenever a
page directory is modified, so add that to tlb_flush().

Fixes: c5e9b2c2 ("riscv: Improve tlb_flush()")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240128120405.25876-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Alexandre Ghiti <alexghiti@rivosinc.com> says:

While merging riscv napot and arm64 contpte support, I noticed we did
not abide by the specification which states that we should clear a
napot mapping before setting a new one, called "break before make" in
arm64 (patch 1). And also that we did not add the new hugetlb page size
added by napot in hugetlb_mask_last_page() (patch 2).

* b4-shazam-merge:
  riscv: Fix hugetlb_mask_last_page() when NAPOT is enabled
  riscv: Fix set_huge_pte_at() for NAPOT mapping

Link: https://lore.kernel.org/r/20240117195741.1926459-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

When NAPOT is enabled, a new hugepage size is available and then we need
to make hugetlb_mask_last_page() aware of that.

Fixes: 82a1a1f3 ("riscv: mm: support Svnapot in hugetlb page")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240117195741.1926459-3-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

As stated by the privileged specification, we must clear a NAPOT
mapping and emit a sfence.vma before setting a new translation.

Fixes: 82a1a1f3 ("riscv: mm: support Svnapot in hugetlb page")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240117195741.1926459-2-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

The spare_init() calls memmap_populate() many times to create VA to PA
mapping for the VMEMMAP area, where all "struct page" are located once
CONFIG_SPARSEMEM_VMEMMAP is defined. These "struct page" are later
initialized in the zone_sizes_init() function. However, during this
process, no sfence.vma instruction is executed for this VMEMMAP area.
This omission may cause the hart to fail to perform page table walk
because some data related to the address translation is invisible to the
hart. To solve this issue, the local_flush_tlb_kernel_range() is called
right after the sparse_init() to execute a sfence.vma instruction for this
VMEMMAP area, ensuring that all data related to the address translation
is visible to the hart.

Fixes: d95f1a54 ("RISC-V: Implement sparsemem")
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240117140333.2479667-1-vincent.chen@sifive.com
Fixes: 7a92fc8b ("mm: Introduce flush_cache_vmap_early()")
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

If non-leaf PTEs I.E pmd, pud or p4d is modified, a sfence.vma is
a must for safe, imagine if an implementation caches the non-leaf
translation in TLB, although I didn't meet this HW so far, but it's
possible in theory.
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Fixes: c5e9b2c2 ("riscv: Improve tlb_flush()")
Link: https://lore.kernel.org/r/20231219175046.2496-2-jszhang@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Pull more bcachefs updates from Kent Overstreet:
 "Some fixes, Some refactoring, some minor features:

   - Assorted prep work for disk space accounting rewrite

   - BTREE_TRIGGER_ATOMIC: after combining our trigger callbacks, this
     makes our trigger context more explicit

   - A few fixes to avoid excessive transaction restarts on
     multithreaded workloads: fstests (in addition to ktest tests) are
     now checking slowpath counters, and that's shaking out a few bugs

   - Assorted tracepoint improvements

   - Starting to break up bcachefs_format.h and move on disk types so
     they're with the code they belong to; this will make room to start
     documenting the on disk format better.

   - A few minor fixes"

* tag 'bcachefs-2024-01-21' of https://evilpiepirate.org/git/bcachefs: (46 commits)
  bcachefs: Improve inode_to_text()
  bcachefs: logged_ops_format.h
  bcachefs: reflink_format.h
  bcachefs; extents_format.h
  bcachefs: ec_format.h
  bcachefs: subvolume_format.h
  bcachefs: snapshot_format.h
  bcachefs: alloc_background_format.h
  bcachefs: xattr_format.h
  bcachefs: dirent_format.h
  bcachefs: inode_format.h
  bcachefs; quota_format.h
  bcachefs: sb-counters_format.h
  bcachefs: counters.c -> sb-counters.c
  bcachefs: comment bch_subvolume
  bcachefs: bch_snapshot::btime
  bcachefs: add missing __GFP_NOWARN
  bcachefs: opts->compression can now also be applied in the background
  bcachefs: Prep work for variable size btree node buffers
  bcachefs: grab s_umount only if snapshotting
  ...

Pull timer updates from Thomas Gleixner:
 "Updates for time and clocksources:

   - A fix for the idle and iowait time accounting vs CPU hotplug.

     The time is reset on CPU hotplug which makes the accumulated
     systemwide time jump backwards.

   - Assorted fixes and improvements for clocksource/event drivers"

* tag 'timers-core-2024-01-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tick-sched: Fix idle and iowait sleeptime accounting vs CPU hotplug
  clocksource/drivers/ep93xx: Fix error handling during probe
  clocksource/drivers/cadence-ttc: Fix some kernel-doc warnings
  clocksource/drivers/timer-ti-dm: Fix make W=n kerneldoc warnings
  clocksource/timer-riscv: Add riscv_clock_shutdown callback
  dt-bindings: timer: Add StarFive JH8100 clint
  dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs

Pull powerpc fixes from Aneesh Kumar:

 - Increase default stack size to 32KB for Book3S

Thanks to Michael Ellerman.

* tag 'powerpc-6.8-2' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  powerpc/64s: Increase default stack size to 32KB

Add line breaks - inode_to_text() is now much easier to read.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs_format.h has gotten too big; let's do some organizing.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Add a field to bch_snapshot for creation time; this will be important
when we start exposing the snapshot tree to userspace.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

The "apply this compression method in the background" paths now use the
compression option if background_compression is not set; this means that
setting or changing the compression option will cause existing data to
be compressed accordingly in the background.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs btree nodes are big - typically 256k - and btree roots are
pinned in memory. As we're now up to 18 btrees, we now have significant
memory overhead in mostly empty btree roots.

And in the future we're going to start enforcing that certain btree node
boundaries exist, to solve lock contention issues - analagous to XFS's
AGIs.

Thus, we need to start allocating smaller btree node buffers when we
can. This patch changes code that refers to the filesystem constant
c->opts.btree_node_size to refer to the btree node buffer size -
btree_buf_bytes() - where appropriate.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

When I was testing mongodb over bcachefs with compression,
there is a lockdep warning when snapshotting mongodb data volume.

$ cat test.sh
prog=bcachefs

$prog subvolume create /mnt/data
$prog subvolume create /mnt/data/snapshots

while true;do
    $prog subvolume snapshot /mnt/data /mnt/data/snapshots/$(date +%s)
    sleep 1s
done

$ cat /etc/mongodb.conf
systemLog:
  destination: file
  logAppend: true
  path: /mnt/data/mongod.log

storage:
  dbPath: /mnt/data/

lockdep reports:
[ 3437.452330] ======================================================
[ 3437.452750] WARNING: possible circular locking dependency detected
[ 3437.453168] 6.7.0-rc7-custom+ #85 Tainted: G            E
[ 3437.453562] ------------------------------------------------------
[ 3437.453981] bcachefs/35533 is trying to acquire lock:
[ 3437.454325] ffffa0a02b2b1418 (sb_writers#10){.+.+}-{0:0}, at: filename_create+0x62/0x190
[ 3437.454875]
               but task is already holding lock:
[ 3437.455268] ffffa0a02b2b10e0 (&type->s_umount_key#48){.+.+}-{3:3}, at: bch2_fs_file_ioctl+0x232/0xc90 [bcachefs]
[ 3437.456009]
               which lock already depends on the new lock.

[ 3437.456553]
               the existing dependency chain (in reverse order) is:
[ 3437.457054]
               -> #3 (&type->s_umount_key#48){.+.+}-{3:3}:
[ 3437.457507]        down_read+0x3e/0x170
[ 3437.457772]        bch2_fs_file_ioctl+0x232/0xc90 [bcachefs]
[ 3437.458206]        __x64_sys_ioctl+0x93/0xd0
[ 3437.458498]        do_syscall_64+0x42/0xf0
[ 3437.458779]        entry_SYSCALL_64_after_hwframe+0x6e/0x76
[ 3437.459155]
               -> #2 (&c->snapshot_create_lock){++++}-{3:3}:
[ 3437.459615]        down_read+0x3e/0x170
[ 3437.459878]        bch2_truncate+0x82/0x110 [bcachefs]
[ 3437.460276]        bchfs_truncate+0x254/0x3c0 [bcachefs]
[ 3437.460686]        notify_change+0x1f1/0x4a0
[ 3437.461283]        do_truncate+0x7f/0xd0
[ 3437.461555]        path_openat+0xa57/0xce0
[ 3437.461836]        do_filp_open+0xb4/0x160
[ 3437.462116]        do_sys_openat2+0x91/0xc0
[ 3437.462402]        __x64_sys_openat+0x53/0xa0
[ 3437.462701]        do_syscall_64+0x42/0xf0
[ 3437.462982]        entry_SYSCALL_64_after_hwframe+0x6e/0x76
[ 3437.463359]
               -> #1 (&sb->s_type->i_mutex_key#15){+.+.}-{3:3}:
[ 3437.463843]        down_write+0x3b/0xc0
[ 3437.464223]        bch2_write_iter+0x5b/0xcc0 [bcachefs]
[ 3437.464493]        vfs_write+0x21b/0x4c0
[ 3437.464653]        ksys_write+0x69/0xf0
[ 3437.464839]        do_syscall_64+0x42/0xf0
[ 3437.465009]        entry_SYSCALL_64_after_hwframe+0x6e/0x76
[ 3437.465231]
               -> #0 (sb_writers#10){.+.+}-{0:0}:
[ 3437.465471]        __lock_acquire+0x1455/0x21b0
[ 3437.465656]        lock_acquire+0xc6/0x2b0
[ 3437.465822]        mnt_want_write+0x46/0x1a0
[ 3437.465996]        filename_create+0x62/0x190
[ 3437.466175]        user_path_create+0x2d/0x50
[ 3437.466352]        bch2_fs_file_ioctl+0x2ec/0xc90 [bcachefs]
[ 3437.466617]        __x64_sys_ioctl+0x93/0xd0
[ 3437.466791]        do_syscall_64+0x42/0xf0
[ 3437.466957]        entry_SYSCALL_64_after_hwframe+0x6e/0x76
[ 3437.467180]
               other info that might help us debug this:

[ 3437.469670] 2 locks held by bcachefs/35533:
               other info that might help us debug this:

[ 3437.467507] Chain exists of:
                 sb_writers#10 --> &c->snapshot_create_lock --> &type->s_umount_key#48

[ 3437.467979]  Possible unsafe locking scenario:

[ 3437.468223]        CPU0                    CPU1
[ 3437.468405]        ----                    ----
[ 3437.468585]   rlock(&type->s_umount_key#48);
[ 3437.468758]                                lock(&c->snapshot_create_lock);
[ 3437.469030]                                lock(&type->s_umount_key#48);
[ 3437.469291]   rlock(sb_writers#10);
[ 3437.469434]
                *** DEADLOCK ***

[ 3437.469670] 2 locks held by bcachefs/35533:
[ 3437.469838]  #0: ffffa0a02ce00a88 (&c->snapshot_create_lock){++++}-{3:3}, at: bch2_fs_file_ioctl+0x1e3/0xc90 [bcachefs]
[ 3437.470294]  #1: ffffa0a02b2b10e0 (&type->s_umount_key#48){.+.+}-{3:3}, at: bch2_fs_file_ioctl+0x232/0xc90 [bcachefs]
[ 3437.470744]
               stack backtrace:
[ 3437.470922] CPU: 7 PID: 35533 Comm: bcachefs Kdump: loaded Tainted: G            E      6.7.0-rc7-custom+ #85
[ 3437.471313] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
[ 3437.471694] Call Trace:
[ 3437.471795]  <TASK>
[ 3437.471884]  dump_stack_lvl+0x57/0x90
[ 3437.472035]  check_noncircular+0x132/0x150
[ 3437.472202]  __lock_acquire+0x1455/0x21b0
[ 3437.472369]  lock_acquire+0xc6/0x2b0
[ 3437.472518]  ? filename_create+0x62/0x190
[ 3437.472683]  ? lock_is_held_type+0x97/0x110
[ 3437.472856]  mnt_want_write+0x46/0x1a0
[ 3437.473025]  ? filename_create+0x62/0x190
[ 3437.473204]  filename_create+0x62/0x190
[ 3437.473380]  user_path_create+0x2d/0x50
[ 3437.473555]  bch2_fs_file_ioctl+0x2ec/0xc90 [bcachefs]
[ 3437.473819]  ? lock_acquire+0xc6/0x2b0
[ 3437.474002]  ? __fget_files+0x2a/0x190
[ 3437.474195]  ? __fget_files+0xbc/0x190
[ 3437.474380]  ? lock_release+0xc5/0x270
[ 3437.474567]  ? __x64_sys_ioctl+0x93/0xd0
[ 3437.474764]  ? __pfx_bch2_fs_file_ioctl+0x10/0x10 [bcachefs]
[ 3437.475090]  __x64_sys_ioctl+0x93/0xd0
[ 3437.475277]  do_syscall_64+0x42/0xf0
[ 3437.475454]  entry_SYSCALL_64_after_hwframe+0x6e/0x76
[ 3437.475691] RIP: 0033:0x7f2743c313af
======================================================

In __bch2_ioctl_subvolume_create(), we grab s_umount unconditionally
and unlock it at the end of the function. There is a comment
"why do we need this lock?" about the lock coming from
commit 42d23732 ("bcachefs: Snapshot creation, deletion")
The reason is that __bch2_ioctl_subvolume_create() calls
sync_inodes_sb() which enforce locked s_umount to writeback all dirty
nodes before doing snapshot works.

Fix it by read locking s_umount for snapshotting only and unlocking
s_umount after sync_inodes_sb().
Signed-off-by: Su Yue <glass.su@suse.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>