1. 23 Jun, 2017 4 commits
    • Richard Cochran's avatar
      net: dp83640: Avoid NULL pointer dereference. · db9d8b29
      Richard Cochran authored
      The function, skb_complete_tx_timestamp(), used to allow passing in a
      NULL pointer for the time stamps, but that was changed in commit
      62bccb8c ("net-timestamp: Make the
      clone operation stand-alone from phy timestamping"), and the existing
      call sites, all of which are in the dp83640 driver, were fixed up.
      
      Even though the kernel-doc was subsequently updated in commit
      7a76a021 ("net-timestamp: Update
      skb_complete_tx_timestamp comment"), still a bug fix from Manfred
      Rudigier came into the driver using the old semantics.  Probably
      Manfred derived that patch from an older kernel version.
      
      This fix should be applied to the stable trees as well.
      
      Fixes: 81e8f2e9 ("net: dp83640: Fix tx timestamp overflow handling.")
      Signed-off-by: default avatarRichard Cochran <richardcochran@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      db9d8b29
    • David S. Miller's avatar
      Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec · 43b786c6
      David S. Miller authored
      Steffen Klassert says:
      
      ====================
      pull request (net): ipsec 2017-06-23
      
      1) Fix xfrm garbage collecting when unregistering a netdevice.
         From Hangbin Liu.
      
      2) Fix NULL pointer derefernce when exiting a network namespace.
         From Hangbin Liu.
      
      3) Fix some error codes in pfkey to prevent a NULL pointer derefernce.
         From Dan Carpenter.
      
      4) Fix NULL pointer derefernce on allocation failure in pfkey.
         From Dan Carpenter.
      
      5) Adjust IPv6 payload_len to include extension headers. Otherwise
         we corrupt the packets when doing ESP GRO on transport mode.
         From Yossi Kuperman.
      
      6) Set nhoff to the proper offset of the IPv6 nexthdr when doing ESP GRO.
         From Yossi Kuperman.
      
      Please pull or let me know if there are problems.
      ====================
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      43b786c6
    • WANG Cong's avatar
      sit: use __GFP_NOWARN for user controlled allocation · 0ccc22f4
      WANG Cong authored
      The memory allocation size is controlled by user-space,
      if it is too large just fail silently and return NULL,
      not to mention there is a fallback allocation later.
      Reported-by: default avatarAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
      Tested-by: default avatarAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      0ccc22f4
    • Michal Kubeček's avatar
      net: account for current skb length when deciding about UFO · a5cb659b
      Michal Kubeček authored
      Our customer encountered stuck NFS writes for blocks starting at specific
      offsets w.r.t. page boundary caused by networking stack sending packets via
      UFO enabled device with wrong checksum. The problem can be reproduced by
      composing a long UDP datagram from multiple parts using MSG_MORE flag:
      
        sendto(sd, buff, 1000, MSG_MORE, ...);
        sendto(sd, buff, 1000, MSG_MORE, ...);
        sendto(sd, buff, 3000, 0, ...);
      
      Assume this packet is to be routed via a device with MTU 1500 and
      NETIF_F_UFO enabled. When second sendto() gets into __ip_append_data(),
      this condition is tested (among others) to decide whether to call
      ip_ufo_append_data():
      
        ((length + fragheaderlen) > mtu) || (skb && skb_is_gso(skb))
      
      At the moment, we already have skb with 1028 bytes of data which is not
      marked for GSO so that the test is false (fragheaderlen is usually 20).
      Thus we append second 1000 bytes to this skb without invoking UFO. Third
      sendto(), however, has sufficient length to trigger the UFO path so that we
      end up with non-UFO skb followed by a UFO one. Later on, udp_send_skb()
      uses udp_csum() to calculate the checksum but that assumes all fragments
      have correct checksum in skb->csum which is not true for UFO fragments.
      
      When checking against MTU, we need to add skb->len to length of new segment
      if we already have a partially filled skb and fragheaderlen only if there
      isn't one.
      
      In the IPv6 case, skb can only be null if this is the first segment so that
      we have to use headersize (length of the first IPv6 header) rather than
      fragheaderlen (length of IPv6 header of further fragments) for skb == NULL.
      
      Fixes: e89e9cf5 ("[IPv4/IPv6]: UFO Scatter-gather approach")
      Fixes: e4c5e13a ("ipv6: Should use consistent conditional judgement for
      	ip6 fragment between __ip6_append_data and ip6_finish_output")
      Signed-off-by: default avatarMichal Kubecek <mkubecek@suse.cz>
      Acked-by: default avatarVlad Yasevich <vyasevic@redhat.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      a5cb659b
  2. 22 Jun, 2017 15 commits
  3. 21 Jun, 2017 7 commits
    • Linus Torvalds's avatar
      Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net · 48b6bbef
      Linus Torvalds authored
      Pull networking fixes from David Miller:
      
       1) Fix refcounting wrt timers which hold onto inet6 address objects,
          from Xin Long.
      
       2) Fix an ancient bug in wireless wext ioctls, from Johannes Berg.
      
       3) Firmware handling fixes in brcm80211 driver, from Arend Van Spriel.
      
       4) Several mlx5 driver fixes (firmware readiness, timestamp cap
          reporting, devlink command validity checking, tc offloading, etc.)
          From Eli Cohen, Maor Dickman, Chris Mi, and Or Gerlitz.
      
       5) Fix dst leak in IP/IP6 tunnels, from Haishuang Yan.
      
       6) Fix dst refcount bug in decnet, from Wei Wang.
      
       7) Netdev can be double freed in register_vlan_device(). Fix from Gao
          Feng.
      
       8) Don't allow object to be destroyed while it is being dumped in SCTP,
          from Xin Long.
      
       9) Fix dpaa_eth build when modular, from Madalin Bucur.
      
      10) Fix throw route leaks, from Serhey Popovych.
      
      11) IFLA_GROUP missing from if_nlmsg_size() and ifla_policy[] table,
          also from Serhey Popovych.
      
      12) Fix premature TX SKB free in stmmac, from Niklas Cassel.
      
      * git://git.kernel.org/pub/scm/linux/kernel/git/davem/net: (36 commits)
        igmp: add a missing spin_lock_init()
        net: stmmac: free an skb first when there are no longer any descriptors using it
        sfc: remove duplicate up_write on VF filter_sem
        rtnetlink: add IFLA_GROUP to ifla_policy
        ipv6: Do not leak throw route references
        dt-bindings: net: sms911x: Add missing optional VDD regulators
        dpaa_eth: reuse the dma_ops provided by the FMan MAC device
        fsl/fman: propagate dma_ops
        net/core: remove explicit do_softirq() from busy_poll_stop()
        fib_rules: Resolve goto rules target on delete
        sctp: ensure ep is not destroyed before doing the dump
        net/hns:bugfix of ethtool -t phy self_test
        net: 8021q: Fix one possible panic caused by BUG_ON in free_netdev
        cxgb4: notify uP to route ctrlq compl to rdma rspq
        ip6_tunnel: Correct tos value in collect_md mode
        decnet: always not take dst->__refcnt when inserting dst into hash table
        ip6_tunnel: fix potential issue in __ip6_tnl_rcv
        ip_tunnel: fix potential issue in ip_tunnel_rcv
        brcmfmac: fix uninitialized warning in brcmf_usb_probe_phase2()
        net/mlx5e: Avoid doing a cleanup call if the profile doesn't have it
        ...
      48b6bbef
    • Linus Torvalds's avatar
      Merge tag 'pinctrl-v4.12-3' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl · ce879b64
      Linus Torvalds authored
      Pull more pin control fixes from Linus Walleij:
       "Some late arriving fixes. I should have sent earlier, just swamped
        with work as usual. Thomas patch makes AMD systems usable despite
        firmware bugs so it is fairly important.
      
         - Make the AMD driver use a regular interrupt rather than a chained
           one, so the system does not lock up.
      
         - Fix a function call error deep inside the STM32 driver"
      
      * tag 'pinctrl-v4.12-3' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl:
        pinctrl: stm32: Fix bad function call
        pinctrl/amd: Use regular interrupt instead of chained
      ce879b64
    • Linus Torvalds's avatar
      Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid · db1b5ccd
      Linus Torvalds authored
      Pull HID fixes from Jiri Kosina:
      
       - revert of a commit to magicmouse driver that regressess certain
         devices, from Daniel Stone
      
       - quirk for a specific Dell mouse, from Sebastian Parschauer
      
      * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid:
        Revert "HID: magicmouse: Set multi-touch keybits for Magic Mouse"
        HID: Add quirk for Dell PIXART OEM mouse
      db1b5ccd
    • Linus Torvalds's avatar
      Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching · dcba7108
      Linus Torvalds authored
      Pull livepatching fix from Jiri Kosina:
       "Fix the way how livepatches are being stacked with respect to RCU,
        from Petr Mladek"
      
      * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
        livepatch: Fix stacking of patches with respect to RCU
      dcba7108
    • Linus Torvalds's avatar
      Merge branch 'ufs-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs · 021f6019
      Linus Torvalds authored
      Pull more ufs fixes from Al Viro:
       "More UFS fixes, unfortunately including build regression fix for the
        64-bit s_dsize commit. Fixed in this pile:
      
         - trivial bug in signedness of 32bit timestamps on ufs1
      
         - ESTALE instead of ufs_error() when doing open-by-fhandle on
           something deleted
      
         - build regression on 32bit in ufs_new_fragments() - calculating that
           many percents of u64 pulls libgcc stuff on some of those. Mea
           culpa.
      
         - fix hysteresis loop broken by typo in 2.4.14.7 (right next to the
           location of previous bug).
      
         - fix the insane limits of said hysteresis loop on filesystems with
           very low percentage of reserved blocks. If it's 5% or less, just
           use the OPTSPACE policy.
      
         - calculate those limits once and mount time.
      
        This tree does pass xfstests clean (both ufs1 and ufs2) and it _does_
        survive cross-builds.
      
        Again, my apologies for missing that, especially since I have noticed
        a related percentage-of-64bit issue in earlier patches (when dealing
        with amount of reserved blocks). Self-LART applied..."
      
      * 'ufs-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
        ufs: fix the logics for tail relocation
        ufs_iget(): fail with -ESTALE on deleted inode
        fix signedness of timestamps on ufs1
      021f6019
    • Helge Deller's avatar
      Allow stack to grow up to address space limit · bd726c90
      Helge Deller authored
      Fix expand_upwards() on architectures with an upward-growing stack (parisc,
      metag and partly IA-64) to allow the stack to reliably grow exactly up to
      the address space limit given by TASK_SIZE.
      Signed-off-by: default avatarHelge Deller <deller@gmx.de>
      Acked-by: default avatarHugh Dickins <hughd@google.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      bd726c90
    • Hugh Dickins's avatar
      mm: fix new crash in unmapped_area_topdown() · f4cb767d
      Hugh Dickins authored
      Trinity gets kernel BUG at mm/mmap.c:1963! in about 3 minutes of
      mmap testing.  That's the VM_BUG_ON(gap_end < gap_start) at the
      end of unmapped_area_topdown().  Linus points out how MAP_FIXED
      (which does not have to respect our stack guard gap intentions)
      could result in gap_end below gap_start there.  Fix that, and
      the similar case in its alternative, unmapped_area().
      
      Cc: stable@vger.kernel.org
      Fixes: 1be7107f ("mm: larger stack guard gap, between vmas")
      Reported-by: default avatarDave Jones <davej@codemonkey.org.uk>
      Debugged-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarHugh Dickins <hughd@google.com>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      f4cb767d
  4. 20 Jun, 2017 14 commits
    • WANG Cong's avatar
      igmp: add a missing spin_lock_init() · b4846fc3
      WANG Cong authored
      Andrey reported a lockdep warning on non-initialized
      spinlock:
      
       INFO: trying to register non-static key.
       the code is fine but needs lockdep annotation.
       turning off the locking correctness validator.
       CPU: 1 PID: 4099 Comm: a.out Not tainted 4.12.0-rc6+ #9
       Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
       Call Trace:
        __dump_stack lib/dump_stack.c:16
        dump_stack+0x292/0x395 lib/dump_stack.c:52
        register_lock_class+0x717/0x1aa0 kernel/locking/lockdep.c:755
        ? 0xffffffffa0000000
        __lock_acquire+0x269/0x3690 kernel/locking/lockdep.c:3255
        lock_acquire+0x22d/0x560 kernel/locking/lockdep.c:3855
        __raw_spin_lock_bh ./include/linux/spinlock_api_smp.h:135
        _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:175
        spin_lock_bh ./include/linux/spinlock.h:304
        ip_mc_clear_src+0x27/0x1e0 net/ipv4/igmp.c:2076
        igmpv3_clear_delrec+0xee/0x4f0 net/ipv4/igmp.c:1194
        ip_mc_destroy_dev+0x4e/0x190 net/ipv4/igmp.c:1736
      
      We miss a spin_lock_init() in igmpv3_add_delrec(), probably
      because previously we never use it on this code path. Since
      we already unlink it from the global mc_tomb list, it is
      probably safe not to acquire this spinlock here. It does not
      harm to have it although, to avoid conditional locking.
      
      Fixes: c38b7d32 ("igmp: acquire pmc lock for ip_mc_clear_src()")
      Reported-by: default avatarAndrey Konovalov <andreyknvl@google.com>
      Signed-off-by: default avatarCong Wang <xiyou.wangcong@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      b4846fc3
    • David S. Miller's avatar
      Merge tag 'wireless-drivers-for-davem-2017-06-20' of... · afd64631
      David S. Miller authored
      Merge tag 'wireless-drivers-for-davem-2017-06-20' of git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/wireless-drivers
      
      Kalle Valo says:
      
      ====================
      wireless-drivers fixes for 4.12
      
      Two important fixes for brcmfmac. The rest of the brcmfmac patches are
      either code preparation and fixing a new build warning.
      
      brcmfmac
      
      * fix a NULL pointer dereference during resume
      
      * fix a NULL pointer dereference with USB devices, a regression from
        v4.12-rc1
      ====================
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      afd64631
    • Niklas Cassel's avatar
      net: stmmac: free an skb first when there are no longer any descriptors using it · 05cf0d1b
      Niklas Cassel authored
      When having the skb pointer in the first descriptor, stmmac_tx_clean
      can get called at a moment where the IP has only cleared the own bit
      of the first descriptor, thus freeing the skb, even though there can
      be several descriptors whose buffers point into the same skb.
      
      By simply moving the skb pointer from the first descriptor to the last
      descriptor, a skb will get freed only when the IP has cleared the
      own bit of all the descriptors that are using that skb.
      Signed-off-by: default avatarNiklas Cassel <niklas.cassel@axis.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      05cf0d1b
    • Edward Cree's avatar
      sfc: remove duplicate up_write on VF filter_sem · 57f0c9cf
      Edward Cree authored
      Somehow two copies of the line 'up_write(&vf->efx->filter_sem);' got into
       efx_ef10_sriov_set_vf_vlan().  This would put the mutex in a bad state and
       cause all subsequent down attempts to hang.
      
      Fixes: 671b53ee ("sfc: Ensure down_write(&filter_sem) and up_write() are matched before calling efx_net_open()")
      Signed-off-by: default avatarEdward Cree <ecree@solarflare.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      57f0c9cf
    • Serhey Popovych's avatar
      rtnetlink: add IFLA_GROUP to ifla_policy · db833d40
      Serhey Popovych authored
      Network interface groups support added while ago, however
      there is no IFLA_GROUP attribute description in policy
      and netlink message size calculations until now.
      
      Add IFLA_GROUP attribute to the policy.
      
      Fixes: cbda10fa ("net_device: add support for network device groups")
      Signed-off-by: default avatarSerhey Popovych <serhe.popovych@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      db833d40
    • Serhey Popovych's avatar
      ipv6: Do not leak throw route references · 07f61557
      Serhey Popovych authored
      While commit 73ba57bf ("ipv6: fix backtracking for throw routes")
      does good job on error propagation to the fib_rules_lookup()
      in fib rules core framework that also corrects throw routes
      handling, it does not solve route reference leakage problem
      happened when we return -EAGAIN to the fib_rules_lookup()
      and leave routing table entry referenced in arg->result.
      
      If rule with matched throw route isn't last matched in the
      list we overwrite arg->result losing reference on throw
      route stored previously forever.
      
      We also partially revert commit ab997ad4 ("ipv6: fix the
      incorrect return value of throw route") since we never return
      routing table entry with dst.error == -EAGAIN when
      CONFIG_IPV6_MULTIPLE_TABLES is on. Also there is no point
      to check for RTF_REJECT flag since it is always set throw
      route.
      
      Fixes: 73ba57bf ("ipv6: fix backtracking for throw routes")
      Signed-off-by: default avatarSerhey Popovych <serhe.popovych@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      07f61557
    • Krzysztof Kozlowski's avatar
      dt-bindings: net: sms911x: Add missing optional VDD regulators · 7e113321
      Krzysztof Kozlowski authored
      The lan911x family of devices require supplying from 3.3 V power
      supplies (connected to VDD_IO, VDD_A and VREG_3.3 pins).  The existing
      driver however obtains only VDD_IO and VDD_A regulators in an optional
      way so document this in bindings.
      Signed-off-by: default avatarKrzysztof Kozlowski <krzk@kernel.org>
      Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      7e113321
    • David S. Miller's avatar
      Merge branch 'net-fix-loadable-module-for-DPAA-Ethernet' · 73b098d6
      David S. Miller authored
      Madalin Bucur says:
      
      ====================
      net: fix loadable module for DPAA Ethernet
      
      The DPAA Ethernet makes use of a symbol that is not exported.
      Address the issue by propagating the dma_ops rather than calling
      arch_setup_dma_ops().
      ====================
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      73b098d6
    • Madalin Bucur's avatar
      dpaa_eth: reuse the dma_ops provided by the FMan MAC device · fb52728a
      Madalin Bucur authored
      Remove the use of arch_setup_dma_ops() that was not exported
      and was breaking loadable module compilation.
      Signed-off-by: default avatarMadalin Bucur <madalin.bucur@nxp.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      fb52728a
    • Madalin Bucur's avatar
      fsl/fman: propagate dma_ops · 5567e989
      Madalin Bucur authored
      Make sure dma_ops are set, to be later used by the Ethernet driver.
      Signed-off-by: default avatarMadalin Bucur <madalin.bucur@nxp.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      5567e989
    • Sebastian Siewior's avatar
      net/core: remove explicit do_softirq() from busy_poll_stop() · fe420d87
      Sebastian Siewior authored
      Since commit 217f6974 ("net: busy-poll: allow preemption in
      sk_busy_loop()") there is an explicit do_softirq() invocation after
      local_bh_enable() has been invoked.
      I don't understand why we need this because local_bh_enable() will
      invoke do_softirq() once the softirq counter reached zero and we have
      softirq-related work pending.
      Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      fe420d87
    • Serhey Popovych's avatar
      fib_rules: Resolve goto rules target on delete · bdaf32c3
      Serhey Popovych authored
      We should avoid marking goto rules unresolved when their
      target is actually reachable after rule deletion.
      
      Consolder following sample scenario:
      
        # ip -4 ru sh
        0:      from all lookup local
        32000:  from all goto 32100
        32100:  from all lookup main
        32100:  from all lookup default
        32766:  from all lookup main
        32767:  from all lookup default
      
        # ip -4 ru del pref 32100 table main
        # ip -4 ru sh
        0:      from all lookup local
        32000:  from all goto 32100 [unresolved]
        32100:  from all lookup default
        32766:  from all lookup main
        32767:  from all lookup default
      
      After removal of first rule with preference 32100 we
      mark all goto rules as unreachable, even when rule with
      same preference as removed one still present.
      
      Check if next rule with same preference is available
      and make all rules with goto action pointing to it.
      Signed-off-by: default avatarSerhey Popovych <serhe.popovych@gmail.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      bdaf32c3
    • Jiri Kosina's avatar
      900a88ef
    • Petr Mladek's avatar
      livepatch: Fix stacking of patches with respect to RCU · 842c0884
      Petr Mladek authored
      rcu_read_(un)lock(), list_*_rcu(), and synchronize_rcu() are used for a secure
      access and manipulation of the list of patches that modify the same function.
      In particular, it is the variable func_stack that is accessible from the ftrace
      handler via struct ftrace_ops and klp_ops.
      
      Of course, it synchronizes also some states of the patch on the top of the
      stack, e.g. func->transition in klp_ftrace_handler.
      
      At the same time, this mechanism guards also the manipulation of
      task->patch_state. It is modified according to the state of the transition and
      the state of the process.
      
      Now, all this works well as long as RCU works well. Sadly livepatching might
      get into some corner cases when this is not true. For example, RCU is not
      watching when rcu_read_lock() is taken in idle threads.  It is because they
      might sleep and prevent reaching the grace period for too long.
      
      There are ways how to make RCU watching even in idle threads, see
      rcu_irq_enter(). But there is a small location inside RCU infrastructure when
      even this does not work.
      
      This small problematic location can be detected either before calling
      rcu_irq_enter() by rcu_irq_enter_disabled() or later by rcu_is_watching().
      Sadly, there is no safe way how to handle it.  Once we detect that RCU was not
      watching, we might see inconsistent state of the function stack and the related
      variables in klp_ftrace_handler(). Then we could do a wrong decision, use an
      incompatible implementation of the function and break the consistency of the
      system. We could warn but we could not avoid the damage.
      
      Fortunately, ftrace has similar problems and they seem to be solved well there.
      It uses a heavy weight implementation of some RCU operations. In particular, it
      replaces:
      
        + rcu_read_lock() with preempt_disable_notrace()
        + rcu_read_unlock() with preempt_enable_notrace()
        + synchronize_rcu() with schedule_on_each_cpu(sync_work)
      
      My understanding is that this is RCU implementation from a stone age. It meets
      the core RCU requirements but it is rather ineffective. Especially, it does not
      allow to batch or speed up the synchronize calls.
      
      On the other hand, it is very trivial. It allows to safely trace and/or
      livepatch even the RCU core infrastructure.  And the effectiveness is a not a
      big issue because using ftrace or livepatches on productive systems is a rare
      operation.  The safety is much more important than a negligible extra load.
      
      Note that the alternative implementation follows the RCU principles. Therefore,
           we could and actually must use list_*_rcu() variants when manipulating the
           func_stack.  These functions allow to access the pointers in the right
           order and with the right barriers. But they do not use any other
           information that would be set only by rcu_read_lock().
      
      Also note that there are actually two problems solved in ftrace:
      
      First, it cares about the consistency of RCU read sections.  It is being solved
      the way as described and used in this patch.
      
      Second, ftrace needs to make sure that nobody is inside the dynamic trampoline
      when it is being freed. For this, it also calls synchronize_rcu_tasks() in
      preemptive kernel in ftrace_shutdown().
      
      Livepatch has similar problem but it is solved by ftrace for free.
      klp_ftrace_handler() is a good guy and never sleeps. In addition, it is
      registered with FTRACE_OPS_FL_DYNAMIC. It causes that
      unregister_ftrace_function() calls:
      
      	* schedule_on_each_cpu(ftrace_sync) - always
      	* synchronize_rcu_tasks() - in preemptive kernel
      
      The effect is that nobody is neither inside the dynamic trampoline nor inside
      the ftrace handler after unregister_ftrace_function() returns.
      
      [jkosina@suse.cz: reformat changelog, fix comment]
      Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
      Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
      Acked-by: default avatarMiroslav Benes <mbenes@suse.cz>
      Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
      842c0884