<feed xmlns='http://www.w3.org/2005/Atom'>
<title>wireguard-linux/kernel, branch jd/orphan-parallel</title>
<subtitle>WireGuard for the Linux kernel</subtitle>
<id>https://git.zx2c4.com/wireguard-linux/atom/kernel?h=jd%2Forphan-parallel</id>
<link rel='self' href='https://git.zx2c4.com/wireguard-linux/atom/kernel?h=jd%2Forphan-parallel'/>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/'/>
<updated>2020-10-23T19:05:49Z</updated>
<entry>
<title>Merge tag 'net-5.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net</title>
<updated>2020-10-23T19:05:49Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2020-10-23T19:05:49Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=3cb12d27ff655e57e8efe3486dca2a22f4e30578'/>
<id>urn:sha1:3cb12d27ff655e57e8efe3486dca2a22f4e30578</id>
<content type='text'>
Pull networking fixes from Jakub Kicinski:
 "Cross-tree/merge window issues:

   - rtl8150: don't incorrectly assign random MAC addresses; fix late in
     the 5.9 cycle started depending on a return code from a function
     which changed with the 5.10 PR from the usb subsystem

  Current release regressions:

   - Revert "virtio-net: ethtool configurable RXCSUM", it was causing
     crashes at probe when control vq was not negotiated/available

  Previous release regressions:

   - ixgbe: fix probing of multi-port 10 Gigabit Intel NICs with an MDIO
     bus, only first device would be probed correctly

   - nexthop: Fix performance regression in nexthop deletion by
     effectively switching from recently added synchronize_rcu() to
     synchronize_rcu_expedited()

   - netsec: ignore 'phy-mode' device property on ACPI systems; the
     property is not populated correctly by the firmware, but firmware
     configures the PHY so just keep boot settings

  Previous releases - always broken:

   - tcp: fix to update snd_wl1 in bulk receiver fast path, addressing
     bulk transfers getting "stuck"

   - icmp: randomize the global rate limiter to prevent attackers from
     getting useful signal

   - r8169: fix operation under forced interrupt threading, make the
     driver always use hard irqs, even on RT, given the handler is light
     and only wants to schedule napi (and do so through a _irqoff()
     variant, preferably)

   - bpf: Enforce pointer id generation for all may-be-null register
     type to avoid pointers erroneously getting marked as null-checked

   - tipc: re-configure queue limit for broadcast link

   - net/sched: act_tunnel_key: fix OOB write in case of IPv6 ERSPAN
     tunnels

   - fix various issues in chelsio inline tls driver

  Misc:

   - bpf: improve just-added bpf_redirect_neigh() helper api to support
     supplying nexthop by the caller - in case BPF program has already
     done a lookup we can avoid doing another one

   - remove unnecessary break statements

   - make MCTCP not select IPV6, but rather depend on it"

* tag 'net-5.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (62 commits)
  tcp: fix to update snd_wl1 in bulk receiver fast path
  net: Properly typecast int values to set sk_max_pacing_rate
  netfilter: nf_fwd_netdev: clear timestamp in forwarding path
  ibmvnic: save changed mac address to adapter-&gt;mac_addr
  selftests: mptcp: depends on built-in IPv6
  Revert "virtio-net: ethtool configurable RXCSUM"
  rtnetlink: fix data overflow in rtnl_calcit()
  net: ethernet: mtk-star-emac: select REGMAP_MMIO
  net: hdlc_raw_eth: Clear the IFF_TX_SKB_SHARING flag after calling ether_setup
  net: hdlc: In hdlc_rcv, check to make sure dev is an HDLC device
  bpf, libbpf: Guard bpf inline asm from bpf_tail_call_static
  bpf, selftests: Extend test_tc_redirect to use modified bpf_redirect_neigh()
  bpf: Fix bpf_redirect_neigh helper api to support supplying nexthop
  mptcp: depends on IPV6 but not as a module
  sfc: move initialisation of efx-&gt;filter_sem to efx_init_struct()
  mpls: load mpls_gso after mpls_iptunnel
  net/sched: act_tunnel_key: fix OOB write in case of IPv6 ERSPAN tunnels
  net/sched: act_gate: Unlock -&gt;tcfa_lock in tc_setup_flow_action()
  net: dsa: bcm_sf2: make const array static, makes object smaller
  mptcp: MPTCP_IPV6 should depend on IPV6 instead of selecting it
  ...
</content>
</entry>
<entry>
<title>Merge tag 'arch-cleanup-2020-10-22' of git://git.kernel.dk/linux-block</title>
<updated>2020-10-23T17:06:38Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2020-10-23T17:06:38Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=4a22709e21c2b1bedf90f68c823daf65d8e6b491'/>
<id>urn:sha1:4a22709e21c2b1bedf90f68c823daf65d8e6b491</id>
<content type='text'>
Pull arch task_work cleanups from Jens Axboe:
 "Two cleanups that don't fit other categories:

   - Finally get the task_work_add() cleanup done properly, so we don't
     have random 0/1/false/true/TWA_SIGNAL confusing use cases. Updates
     all callers, and also fixes up the documentation for
     task_work_add().

   - While working on some TIF related changes for 5.11, this
     TIF_NOTIFY_RESUME cleanup fell out of that. Remove some arch
     duplication for how that is handled"

* tag 'arch-cleanup-2020-10-22' of git://git.kernel.dk/linux-block:
  task_work: cleanup notification modes
  tracehook: clear TIF_NOTIFY_RESUME in tracehook_notify_resume()
</content>
</entry>
<entry>
<title>Merge tag 'kbuild-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild</title>
<updated>2020-10-22T20:13:57Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2020-10-22T20:13:57Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=746b25b1aa0f5736d585728ded70a8141da91edb'/>
<id>urn:sha1:746b25b1aa0f5736d585728ded70a8141da91edb</id>
<content type='text'>
Pull Kbuild updates from Masahiro Yamada:

 - Support 'make compile_commands.json' to generate the compilation
   database more easily, avoiding stale entries

 - Support 'make clang-analyzer' and 'make clang-tidy' for static checks
   using clang-tidy

 - Preprocess scripts/modules.lds.S to allow CONFIG options in the
   module linker script

 - Drop cc-option tests from compiler flags supported by our minimal
   GCC/Clang versions

 - Use always 12-digits commit hash for CONFIG_LOCALVERSION_AUTO=y

 - Use sha1 build id for both BFD linker and LLD

 - Improve deb-pkg for reproducible builds and rootless builds

 - Remove stale, useless scripts/namespace.pl

 - Turn -Wreturn-type warning into error

 - Fix build error of deb-pkg when CONFIG_MODULES=n

 - Replace 'hostname' command with more portable 'uname -n'

 - Various Makefile cleanups

* tag 'kbuild-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (34 commits)
  kbuild: Use uname for LINUX_COMPILE_HOST detection
  kbuild: Only add -fno-var-tracking-assignments for old GCC versions
  kbuild: remove leftover comment for filechk utility
  treewide: remove DISABLE_LTO
  kbuild: deb-pkg: clean up package name variables
  kbuild: deb-pkg: do not build linux-headers package if CONFIG_MODULES=n
  kbuild: enforce -Werror=return-type
  scripts: remove namespace.pl
  builddeb: Add support for all required debian/rules targets
  builddeb: Enable rootless builds
  builddeb: Pass -n to gzip for reproducible packages
  kbuild: split the build log of kallsyms
  kbuild: explicitly specify the build id style
  scripts/setlocalversion: make git describe output more reliable
  kbuild: remove cc-option test of -Werror=date-time
  kbuild: remove cc-option test of -fno-stack-check
  kbuild: remove cc-option test of -fno-strict-overflow
  kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to relevant Makefiles
  kbuild: remove redundant CONFIG_KASAN check from scripts/Makefile.kasan
  kbuild: do not create built-in objects for external module builds
  ...
</content>
</entry>
<entry>
<title>Merge tag 'modules-for-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux</title>
<updated>2020-10-22T20:08:57Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2020-10-22T20:08:57Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=2b71482060e1e6962720dbca1dff702580fa0748'/>
<id>urn:sha1:2b71482060e1e6962720dbca1dff702580fa0748</id>
<content type='text'>
Pull modules updates from Jessica Yu:
 "Code cleanups: more informative error messages and statically
  initialize init_free_wq to avoid a workqueue warning"

* tag 'modules-for-v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/jeyu/linux:
  module: statically initialize init section freeing data
  module: Add more error message for failed kernel module loading
</content>
</entry>
<entry>
<title>Merge branch 'work.set_fs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs</title>
<updated>2020-10-22T16:59:21Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2020-10-22T16:59:21Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=f56e65dff6ad52395ef45738799b4fb70ff43376'/>
<id>urn:sha1:f56e65dff6ad52395ef45738799b4fb70ff43376</id>
<content type='text'>
Pull initial set_fs() removal from Al Viro:
 "Christoph's set_fs base series + fixups"

* 'work.set_fs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fs: Allow a NULL pos pointer to __kernel_read
  fs: Allow a NULL pos pointer to __kernel_write
  powerpc: remove address space overrides using set_fs()
  powerpc: use non-set_fs based maccess routines
  x86: remove address space overrides using set_fs()
  x86: make TASK_SIZE_MAX usable from assembly code
  x86: move PAGE_OFFSET, TASK_SIZE &amp; friends to page_{32,64}_types.h
  lkdtm: remove set_fs-based tests
  test_bitmap: remove user bitmap tests
  uaccess: add infrastructure for kernel builds with set_fs()
  fs: don't allow splice read/write without explicit ops
  fs: don't allow kernel reads and writes without iter ops
  sysctl: Convert to iter interfaces
  proc: add a read_iter method to proc proc_ops
  proc: cleanup the compat vs no compat file ops
  proc: remove a level of indentation in proc_get_inode
</content>
</entry>
<entry>
<title>treewide: remove DISABLE_LTO</title>
<updated>2020-10-20T15:28:53Z</updated>
<author>
<name>Sami Tolvanen</name>
<email>samitolvanen@google.com</email>
</author>
<published>2020-10-13T00:31:45Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=0f6372e522237f39aff63f2e158d629038f26238'/>
<id>urn:sha1:0f6372e522237f39aff63f2e158d629038f26238</id>
<content type='text'>
This change removes all instances of DISABLE_LTO from
Makefiles, as they are currently unused, and the preferred
method of disabling LTO is to filter out the flags instead.

Note added by Masahiro Yamada:
DISABLE_LTO was added as preparation for GCC LTO, but GCC LTO was
not pulled into the mainline. (https://lkml.org/lkml/2014/4/8/272)

Suggested-by: Kees Cook &lt;keescook@chromium.org&gt;
Signed-off-by: Sami Tolvanen &lt;samitolvanen@google.com&gt;
Reviewed-by: Kees Cook &lt;keescook@chromium.org&gt;
Signed-off-by: Masahiro Yamada &lt;masahiroy@kernel.org&gt;
</content>
</entry>
<entry>
<title>bpf: Enforce id generation for all may-be-null register type</title>
<updated>2020-10-19T22:57:42Z</updated>
<author>
<name>Martin KaFai Lau</name>
<email>kafai@fb.com</email>
</author>
<published>2020-10-19T19:42:12Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=93c230e3f5bd6e1d2b2759d582fdfe9c2731473b'/>
<id>urn:sha1:93c230e3f5bd6e1d2b2759d582fdfe9c2731473b</id>
<content type='text'>
The commit af7ec1383361 ("bpf: Add bpf_skc_to_tcp6_sock() helper")
introduces RET_PTR_TO_BTF_ID_OR_NULL and
the commit eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
introduces RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL.
Note that for RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, the reg0-&gt;type
could become PTR_TO_MEM_OR_NULL which is not covered by
BPF_PROBE_MEM.

The BPF_REG_0 will then hold a _OR_NULL pointer type. This _OR_NULL
pointer type requires the bpf program to explicitly do a NULL check first.
After NULL check, the verifier will mark all registers having
the same reg-&gt;id as safe to use.  However, the reg-&gt;id
is not set for those new _OR_NULL return types.  One of the ways
that may be wrong is, checking NULL for one btf_id typed pointer will
end up validating all other btf_id typed pointers because
all of them have id == 0.  The later tests will exercise
this path.

To fix it and also avoid similar issue in the future, this patch
moves the id generation logic out of each individual RET type
test in check_helper_call().  Instead, it does one
reg_type_may_be_null() test and then do the id generation
if needed.

This patch also adds a WARN_ON_ONCE in mark_ptr_or_null_reg()
to catch future breakage.

The _OR_NULL pointer usage in the bpf_iter_reg.ctx_arg_info is
fine because it just happens that the existing id generation after
check_ctx_access() has covered it.  It is also using the
reg_type_may_be_null() to decide if id generation is needed or not.

Fixes: af7ec1383361 ("bpf: Add bpf_skc_to_tcp6_sock() helper")
Fixes: eaa6bcb71ef6 ("bpf: Introduce bpf_per_cpu_ptr()")
Signed-off-by: Martin KaFai Lau &lt;kafai@fb.com&gt;
Signed-off-by: Alexei Starovoitov &lt;ast@kernel.org&gt;
Link: https://lore.kernel.org/bpf/20201019194212.1050855-1-kafai@fb.com
</content>
</entry>
<entry>
<title>bpf: Remove unneeded break</title>
<updated>2020-10-19T18:40:21Z</updated>
<author>
<name>Tom Rix</name>
<email>trix@redhat.com</email>
</author>
<published>2020-10-19T17:38:46Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=76702a2e7280594a0add4c1283623c81a868373f'/>
<id>urn:sha1:76702a2e7280594a0add4c1283623c81a868373f</id>
<content type='text'>
A break is not needed if it is preceded by a return.

Signed-off-by: Tom Rix &lt;trix@redhat.com&gt;
Signed-off-by: Daniel Borkmann &lt;daniel@iogearbox.net&gt;
Acked-by: Andrii Nakryiko &lt;andrii@kernel.org&gt;
Link: https://lore.kernel.org/bpf/20201019173846.1021-1-trix@redhat.com
</content>
</entry>
<entry>
<title>Merge tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip</title>
<updated>2020-10-18T21:34:50Z</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2020-10-18T21:34:50Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=41eea65e2aaadc0611fd56a1b177ce25dcc4c1df'/>
<id>urn:sha1:41eea65e2aaadc0611fd56a1b177ce25dcc4c1df</id>
<content type='text'>
Pull RCU changes from Ingo Molnar:

 - Debugging for smp_call_function()

 - RT raw/non-raw lock ordering fixes

 - Strict grace periods for KASAN

 - New smp_call_function() torture test

 - Torture-test updates

 - Documentation updates

 - Miscellaneous fixes

[ This doesn't actually pull the tag - I've dropped the last merge from
  the RCU branch due to questions about the series.   - Linus ]

* tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits)
  smp: Make symbol 'csd_bug_count' static
  kernel/smp: Provide CSD lock timeout diagnostics
  smp: Add source and destination CPUs to __call_single_data
  rcu: Shrink each possible cpu krcp
  rcu/segcblist: Prevent useless GP start if no CBs to accelerate
  torture: Add gdb support
  rcutorture: Allow pointer leaks to test diagnostic code
  rcutorture: Hoist OOM registry up one level
  refperf: Avoid null pointer dereference when buf fails to allocate
  rcutorture: Properly synchronize with OOM notifier
  rcutorture: Properly set rcu_fwds for OOM handling
  torture: Add kvm.sh --help and update help message
  rcutorture: Add CONFIG_PROVE_RCU_LIST to TREE05
  torture: Update initrd documentation
  rcutorture: Replace HTTP links with HTTPS ones
  locktorture: Make function torture_percpu_rwsem_init() static
  torture: document --allcpus argument added to the kvm.sh script
  rcutorture: Output number of elapsed grace periods
  rcutorture: Remove KCSAN stubs
  rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp()
  ...
</content>
</entry>
<entry>
<title>mm/madvise: introduce process_madvise() syscall: an external memory hinting API</title>
<updated>2020-10-18T16:27:10Z</updated>
<author>
<name>Minchan Kim</name>
<email>minchan@kernel.org</email>
</author>
<published>2020-10-17T23:14:59Z</published>
<link rel='alternate' type='text/html' href='https://git.zx2c4.com/wireguard-linux/commit/?id=ecb8ac8b1f146915aa6b96449b66dd48984caacc'/>
<id>urn:sha1:ecb8ac8b1f146915aa6b96449b66dd48984caacc</id>
<content type='text'>
There is usecase that System Management Software(SMS) want to give a
memory hint like MADV_[COLD|PAGEEOUT] to other processes and in the
case of Android, it is the ActivityManagerService.

The information required to make the reclaim decision is not known to the
app.  Instead, it is known to the centralized userspace
daemon(ActivityManagerService), and that daemon must be able to initiate
reclaim on its own without any app involvement.

To solve the issue, this patch introduces a new syscall
process_madvise(2).  It uses pidfd of an external process to give the
hint.  It also supports vector address range because Android app has
thousands of vmas due to zygote so it's totally waste of CPU and power if
we should call the syscall one by one for each vma.(With testing 2000-vma
syscall vs 1-vector syscall, it showed 15% performance improvement.  I
think it would be bigger in real practice because the testing ran very
cache friendly environment).

Another potential use case for the vector range is to amortize the cost
ofTLB shootdowns for multiple ranges when using MADV_DONTNEED; this could
benefit users like TCP receive zerocopy and malloc implementations.  In
future, we could find more usecases for other advises so let's make it
happens as API since we introduce a new syscall at this moment.  With
that, existing madvise(2) user could replace it with process_madvise(2)
with their own pid if they want to have batch address ranges support
feature.

ince it could affect other process's address range, only privileged
process(PTRACE_MODE_ATTACH_FSCREDS) or something else(e.g., being the same
UID) gives it the right to ptrace the process could use it successfully.
The flag argument is reserved for future use if we need to extend the API.

I think supporting all hints madvise has/will supported/support to
process_madvise is rather risky.  Because we are not sure all hints make
sense from external process and implementation for the hint may rely on
the caller being in the current context so it could be error-prone.  Thus,
I just limited hints as MADV_[COLD|PAGEOUT] in this patch.

If someone want to add other hints, we could hear the usecase and review
it for each hint.  It's safer for maintenance rather than introducing a
buggy syscall but hard to fix it later.

So finally, the API is as follows,

      ssize_t process_madvise(int pidfd, const struct iovec *iovec,
                unsigned long vlen, int advice, unsigned int flags);

    DESCRIPTION
      The process_madvise() system call is used to give advice or directions
      to the kernel about the address ranges from external process as well as
      local process. It provides the advice to address ranges of process
      described by iovec and vlen. The goal of such advice is to improve
      system or application performance.

      The pidfd selects the process referred to by the PID file descriptor
      specified in pidfd. (See pidofd_open(2) for further information)

      The pointer iovec points to an array of iovec structures, defined in
      &lt;sys/uio.h&gt; as:

        struct iovec {
            void *iov_base;         /* starting address */
            size_t iov_len;         /* number of bytes to be advised */
        };

      The iovec describes address ranges beginning at address(iov_base)
      and with size length of bytes(iov_len).

      The vlen represents the number of elements in iovec.

      The advice is indicated in the advice argument, which is one of the
      following at this moment if the target process specified by pidfd is
      external.

        MADV_COLD
        MADV_PAGEOUT

      Permission to provide a hint to external process is governed by a
      ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).

      The process_madvise supports every advice madvise(2) has if target
      process is in same thread group with calling process so user could
      use process_madvise(2) to extend existing madvise(2) to support
      vector address ranges.

    RETURN VALUE
      On success, process_madvise() returns the number of bytes advised.
      This return value may be less than the total number of requested
      bytes, if an error occurred. The caller should check return value
      to determine whether a partial advice occurred.

FAQ:

Q.1 - Why does any external entity have better knowledge?

Quote from Sandeep

"For Android, every application (including the special SystemServer)
are forked from Zygote.  The reason of course is to share as many
libraries and classes between the two as possible to benefit from the
preloading during boot.

After applications start, (almost) all of the APIs end up calling into
this SystemServer process over IPC (binder) and back to the
application.

In a fully running system, the SystemServer monitors every single
process periodically to calculate their PSS / RSS and also decides
which process is "important" to the user for interactivity.

So, because of how these processes start _and_ the fact that the
SystemServer is looping to monitor each process, it does tend to *know*
which address range of the application is not used / useful.

Besides, we can never rely on applications to clean things up
themselves.  We've had the "hey app1, the system is low on memory,
please trim your memory usage down" notifications for a long time[1].
They rely on applications honoring the broadcasts and very few do.

So, if we want to avoid the inevitable killing of the application and
restarting it, some way to be able to tell the OS about unimportant
memory in these applications will be useful.

- ssp

Q.2 - How to guarantee the race(i.e., object validation) between when
giving a hint from an external process and get the hint from the target
process?

process_madvise operates on the target process's address space as it
exists at the instant that process_madvise is called.  If the space
target process can run between the time the process_madvise process
inspects the target process address space and the time that
process_madvise is actually called, process_madvise may operate on
memory regions that the calling process does not expect.  It's the
responsibility of the process calling process_madvise to close this
race condition.  For example, the calling process can suspend the
target process with ptrace, SIGSTOP, or the freezer cgroup so that it
doesn't have an opportunity to change its own address space before
process_madvise is called.  Another option is to operate on memory
regions that the caller knows a priori will be unchanged in the target
process.  Yet another option is to accept the race for certain
process_madvise calls after reasoning that mistargeting will do no
harm.  The suggested API itself does not provide synchronization.  It
also apply other APIs like move_pages, process_vm_write.

The race isn't really a problem though.  Why is it so wrong to require
that callers do their own synchronization in some manner?  Nobody
objects to write(2) merely because it's possible for two processes to
open the same file and clobber each other's writes --- instead, we tell
people to use flock or something.  Think about mmap.  It never
guarantees newly allocated address space is still valid when the user
tries to access it because other threads could unmap the memory right
before.  That's where we need synchronization by using other API or
design from userside.  It shouldn't be part of API itself.  If someone
needs more fine-grained synchronization rather than process level,
there were two ideas suggested - cookie[2] and anon-fd[3].  Both are
applicable via using last reserved argument of the API but I don't
think it's necessary right now since we have already ways to prevent
the race so don't want to add additional complexity with more
fine-grained optimization model.

To make the API extend, it reserved an unsigned long as last argument
so we could support it in future if someone really needs it.

Q.3 - Why doesn't ptrace work?

Injecting an madvise in the target process using ptrace would not work
for us because such injected madvise would have to be executed by the
target process, which means that process would have to be runnable and
that creates the risk of the abovementioned race and hinting a wrong
VMA.  Furthermore, we want to act the hint in caller's context, not the
callee's, because the callee is usually limited in cpuset/cgroups or
even freezed state so they can't act by themselves quick enough, which
causes more thrashing/kill.  It doesn't work if the target process are
ptraced(e.g., strace, debugger, minidump) because a process can have at
most one ptracer.

[1] https://developer.android.com/topic/performance/memory"

[2] process_getinfo for getting the cookie which is updated whenever
    vma of process address layout are changed - Daniel Colascione -
    https://lore.kernel.org/lkml/20190520035254.57579-1-minchan@kernel.org/T/#m7694416fd179b2066a2c62b5b139b14e3894e224

[3] anonymous fd which is used for the object(i.e., address range)
    validation - Michal Hocko -
    https://lore.kernel.org/lkml/20200120112722.GY18451@dhcp22.suse.cz/

[minchan@kernel.org: fix process_madvise build break for arm64]
  Link: http://lkml.kernel.org/r/20200303145756.GA219683@google.com
[minchan@kernel.org: fix build error for mips of process_madvise]
  Link: http://lkml.kernel.org/r/20200508052517.GA197378@google.com
[akpm@linux-foundation.org: fix patch ordering issue]
[akpm@linux-foundation.org: fix arm64 whoops]
[minchan@kernel.org: make process_madvise() vlen arg have type size_t, per Florian]
[akpm@linux-foundation.org: fix i386 build]
[sfr@canb.auug.org.au: fix syscall numbering]
  Link: https://lkml.kernel.org/r/20200905142639.49fc3f1a@canb.auug.org.au
[sfr@canb.auug.org.au: madvise.c needs compat.h]
  Link: https://lkml.kernel.org/r/20200908204547.285646b4@canb.auug.org.au
[minchan@kernel.org: fix mips build]
  Link: https://lkml.kernel.org/r/20200909173655.GC2435453@google.com
[yuehaibing@huawei.com: remove duplicate header which is included twice]
  Link: https://lkml.kernel.org/r/20200915121550.30584-1-yuehaibing@huawei.com
[minchan@kernel.org: do not use helper functions for process_madvise]
  Link: https://lkml.kernel.org/r/20200921175539.GB387368@google.com
[akpm@linux-foundation.org: pidfd_get_pid() gained an argument]
[sfr@canb.auug.org.au: fix up for "iov_iter: transparently handle compat iovecs in import_iovec"]
  Link: https://lkml.kernel.org/r/20200928212542.468e1fef@canb.auug.org.au

Signed-off-by: Minchan Kim &lt;minchan@kernel.org&gt;
Signed-off-by: YueHaibing &lt;yuehaibing@huawei.com&gt;
Signed-off-by: Stephen Rothwell &lt;sfr@canb.auug.org.au&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Reviewed-by: Suren Baghdasaryan &lt;surenb@google.com&gt;
Reviewed-by: Vlastimil Babka &lt;vbabka@suse.cz&gt;
Acked-by: David Rientjes &lt;rientjes@google.com&gt;
Cc: Alexander Duyck &lt;alexander.h.duyck@linux.intel.com&gt;
Cc: Brian Geffon &lt;bgeffon@google.com&gt;
Cc: Christian Brauner &lt;christian@brauner.io&gt;
Cc: Daniel Colascione &lt;dancol@google.com&gt;
Cc: Jann Horn &lt;jannh@google.com&gt;
Cc: Jens Axboe &lt;axboe@kernel.dk&gt;
Cc: Joel Fernandes &lt;joel@joelfernandes.org&gt;
Cc: Johannes Weiner &lt;hannes@cmpxchg.org&gt;
Cc: John Dias &lt;joaodias@google.com&gt;
Cc: Kirill Tkhai &lt;ktkhai@virtuozzo.com&gt;
Cc: Michal Hocko &lt;mhocko@suse.com&gt;
Cc: Oleksandr Natalenko &lt;oleksandr@redhat.com&gt;
Cc: Sandeep Patil &lt;sspatil@google.com&gt;
Cc: SeongJae Park &lt;sj38.park@gmail.com&gt;
Cc: SeongJae Park &lt;sjpark@amazon.de&gt;
Cc: Shakeel Butt &lt;shakeelb@google.com&gt;
Cc: Sonny Rao &lt;sonnyrao@google.com&gt;
Cc: Tim Murray &lt;timmurray@google.com&gt;
Cc: Christian Brauner &lt;christian.brauner@ubuntu.com&gt;
Cc: Florian Weimer &lt;fw@deneb.enyo.de&gt;
Cc: &lt;linux-man@vger.kernel.org&gt;
Link: http://lkml.kernel.org/r/20200302193630.68771-3-minchan@kernel.org
Link: http://lkml.kernel.org/r/20200508183320.GA125527@google.com
Link: http://lkml.kernel.org/r/20200622192900.22757-4-minchan@kernel.org
Link: https://lkml.kernel.org/r/20200901000633.1920247-4-minchan@kernel.org
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
</entry>
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