1. 05 Dec, 2015 7 commits
  2. 06 Oct, 2015 3 commits
  3. 21 Sep, 2015 1 commit
  4. 22 Jul, 2015 1 commit
  5. 17 Jul, 2015 3 commits
  6. 15 Jul, 2015 1 commit
  7. 22 Jun, 2015 1 commit
  8. 27 May, 2015 3 commits
  9. 16 Jan, 2015 2 commits
    • Paul E. McKenney's avatar
      rcu: Add GP-kthread-starvation checks to CPU stall warnings · fb81a44b
      Paul E. McKenney authored
      This commit adds a message that is printed if the relevant grace-period
      kthread has not been able to run for the two seconds preceding the
      stall warning.  (The two seconds is double the maximum interval between
      successive bouts of quiescent-state forcing.)
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    • Paul E. McKenney's avatar
      rcu: Make cond_resched_rcu_qs() apply to normal RCU flavors · 5cd37193
      Paul E. McKenney authored
      Although cond_resched_rcu_qs() only applies to TASKS_RCU, it is used
      in places where it would be useful for it to apply to the normal RCU
      flavors, rcu_preempt, rcu_sched, and rcu_bh.  This is especially the
      case for workloads that aggressively overload the system, particularly
      those that generate large numbers of RCU updates on systems running
      NO_HZ_FULL CPUs.  This commit therefore communicates quiescent states
      from cond_resched_rcu_qs() to the normal RCU flavors.
      Note that it is unfortunately necessary to leave the old ->passed_quiesce
      mechanism in place to allow quiescent states that apply to only one
      flavor to be recorded.  (Yes, we could decrement ->rcu_qs_ctr_snap in
      that case, but that is not so good for debugging of RCU internals.)
      In addition, if one of the RCU flavor's grace period has stalled, this
      will invoke rcu_momentary_dyntick_idle(), resulting in a heavy-weight
      quiescent state visible from other CPUs.
      Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
      Reported-by: default avatarDave Jones <davej@redhat.com>
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      [ paulmck: Merge commit from Sasha Levin fixing a bug where __this_cpu()
        was used in preemptible code. ]
  10. 06 Jan, 2015 2 commits
    • Paul E. McKenney's avatar
      rcu: Improve diagnostics for spurious RCU CPU stall warnings · 6ccd2ecd
      Paul E. McKenney authored
      The current RCU CPU stall warning code will print "Stall ended before
      state dump start" any time that the stall-warning code is triggered on
      a CPU that has already reported a quiescent state for the current grace
      period and if all quiescent states have been reported for the current
      grace period.  However, a true stall can result in these symptoms, for
      example, by preventing RCU's grace-period kthreads from ever running
      This commit therefore checks for this condition, reporting the end of
      the stall only if one of the grace-period counters has actually advanced.
      Otherwise, it reports the last time that the grace-period kthread made
      meaningful progress.  (In normal situations, the grace-period kthread
      should make meaningful progress at least every jiffies_till_next_fqs
      Reported-by: default avatarMiroslav Benes <mbenes@suse.cz>
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Tested-by: default avatarMiroslav Benes <mbenes@suse.cz>
    • Xie XiuQi's avatar
      documentation: Update sysfs path for rcu_cpu_stall_timeout · 84596ccb
      Xie XiuQi authored
      Commit 6bfc09e2 ("rcu: Provide RCU CPU stall warnings for tiny RCU")
      moved the rcu_cpu_stall_timeout module parameter from rcutree.c to
      rcupdate.c, but failed to update Documentation/RCU/stallwarn.txt. This
      commit therefore repairs this omission.
      commit 96224daa ("documentation: Update sysfs path for rcu_cpu_stall_suppress")
      updated the path for rcu_cpu_stall_suppress, but failed to update for
      Signed-off-by: default avatarXie XiuQi <xiexiuqi@huawei.com>
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
  11. 29 Oct, 2014 1 commit
  12. 28 Oct, 2014 1 commit
    • Paul E. McKenney's avatar
      rcu: Remove CONFIG_RCU_CPU_STALL_VERBOSE · 0eafa468
      Paul E. McKenney authored
      The CONFIG_RCU_CPU_STALL_VERBOSE Kconfig parameter causes preemptible
      RCU's CPU stall warnings to dump out any preempted tasks that are blocking
      the current RCU grace period.  This information is useful, and the default
      has been CONFIG_RCU_CPU_STALL_VERBOSE=y for some years.  It is therefore
      time for this commit to remove this Kconfig parameter, so that future
      kernel builds will always act as if CONFIG_RCU_CPU_STALL_VERBOSE=y.
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
  13. 07 Sep, 2014 1 commit
  14. 07 Aug, 2014 1 commit
    • Ken Helias's avatar
      list: fix order of arguments for hlist_add_after(_rcu) · 1d023284
      Ken Helias authored
      All other add functions for lists have the new item as first argument
      and the position where it is added as second argument.  This was changed
      for no good reason in this function and makes using it unnecessary
      The name was changed to hlist_add_behind() to cause unconverted code to
      generate a compile error instead of using the wrong parameter order.
      [akpm@linux-foundation.org: coding-style fixes]
      Signed-off-by: default avatarKen Helias <kenhelias@firemail.de>
      Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
      Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>	[intel driver bits]
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Christoph Hellwig <hch@infradead.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  15. 08 Jul, 2014 2 commits
  16. 19 Jun, 2014 1 commit
  17. 29 Apr, 2014 3 commits
  18. 17 Feb, 2014 2 commits
  19. 11 Feb, 2014 1 commit
    • Henrik Austad's avatar
      Documentation/: update 00-INDEX files · 3cf8ca1c
      Henrik Austad authored
      Some of the 00-INDEX files are somewhat outdated and some folders does
      not contain 00-INDEX at all.  Only outdated (with the notably exception
      of spi) indexes are touched here, the 169 folders without 00-INDEX has
      not been touched.
      New 00-INDEX
       - spi/* was added in a series of commits dating back to 2006
      Added files (missing in (*/)00-INDEX)
       - dmatest.txt was added by commit 851b7e16 ("dmatest: run test via
       - this_cpu_ops.txt was added by commit a1b2a555 ("percpu: add
         documentation on this_cpu operations")
       - ww-mutex-design.txt was added by commit 040a0a37 ("mutex: Add
         support for wound/wait style locks")
       - bcache.txt was added by commit cafe5635 ("bcache: A block layer
       - kernel-per-CPU-kthreads.txt was added by commit 49717cb4
         ("kthread: Document ways of reducing OS jitter due to per-CPU
       - phy.txt was added by commit ff764963 ("drivers: phy: add generic
         PHY framework")
       - block/null_blk was added by commit 12f8f4fc ("null_blk:
       - module-signing.txt was added by commit 3cafea30 ("Add
         Documentation/module-signing.txt file")
       - assoc_array.txt was added by commit 3cb98950 ("Add a generic
         associative array implementation.")
       - arm/IXP4xx was part of the initial repo
       - arm/cluster-pm-race-avoidance.txt was added by commit 7fe31d28
         ("ARM: mcpm: introduce helpers for platform coherency exit/setup")
       - arm/firmware.txt was added by commit 7366b92a ("ARM: Add
         interface for registering and calling firmware-specific operations")
       - arm/kernel_mode_neon.txt was added by commit 2afd0a05 ("ARM:
         7825/1: document the use of NEON in kernel mode")
       - arm/tcm.txt was added by commit bc581770 ("ARM: 5580/2: ARM TCM
         (Tightly-Coupled Memory) support v3")
       - arm/vlocks.txt was added by commit 9762f12d ("ARM: mcpm: Add
         baremetal voting mutexes")
       - blackfin/gptimers-example.c, Makefile was added by commit
         4b60779d ("Blackfin: add an example showing how to use the
         gptimers API")
       - devicetree/usage-model.txt was added by commit 31134efc ("dt:
         Linux DT usage model documentation")
       - fb/api.txt was added by commit fb21c2f4 ("fbdev: Add FOURCC-based
         format configuration API")
       - fb/sm501.txt was added by commit e6a04980 ("video, sm501: add
         edid and commandline support")
       - fb/udlfb.txt was added by commit 96f8d864 ("fbdev: move udlfb out
         of staging.")
       - filesystems/Makefile was added by commit 1e0051ae
         ("Documentation/fs/: split txt and source files")
       - filesystems/nfs/nfsd-admin-interfaces.txt was added by commit
         8a4c6e19 ("nfsd: document kernel interfaces for nfsd
       - ide/warm-plug-howto.txt was added by commit f74c9141 ("ide: add
         warm-plug support for IDE devices (take 2)")
       - laptops/Makefile was added by commit d49129ac
         ("Documentation/laptop/: split txt and source files")
       - leds/leds-blinkm.txt was added by commit b54cf35a ("LEDS: add
         BlinkM RGB LED driver, documentation and update MAINTAINERS")
       - leds/ledtrig-oneshot.txt was added by commit 5e417281 ("leds: add
         oneshot trigger")
       - leds/ledtrig-transient.txt was added by commit 44e1e9f8 ("leds:
         add new transient trigger for one shot timer activation")
       - m68k/README.buddha was part of the initial repo
       - networking/LICENSE.(qla3xxx|qlcnic|qlge) was added by commits
         40839129, c4e84bde, 5a4faa87
       - networking/Makefile was added by commit 3794f3e8 ("docsrc: build
         Documentation/ sources")
       - networking/i40evf.txt was added by commit 105bf2fe ("i40evf: add
         driver to kernel build system")
       - networking/ipsec.txt was added by commit b3c6efbc ("xfrm: Add
         file to document IPsec corner case")
       - networking/mac80211-auth-assoc-deauth.txt was added by commit
         3cd7920a ("mac80211: add auth/assoc/deauth flow diagram")
       - networking/netlink_mmap.txt was added by commit 5683264c
         ("netlink: add documentation for memory mapped I/O")
       - networking/nf_conntrack-sysctl.txt was added by commit c9f9e0e1
         ("netfilter: doc: add nf_conntrack sysctl api documentation") lan)
       - networking/team.txt was added by commit 3d249d4c ("net: introduce
         ethernet teaming device")
       - networking/vxlan.txt was added by commit d342894c ("vxlan:
         virtual extensible lan")
       - power/runtime_pm.txt was added by commit 5e928f77 ("PM: Introduce
         core framework for run-time PM of I/O devices (rev.  17)")
       - power/charger-manager.txt was added by commit 3bb3dbbd
         ("power_supply: Add initial Charger-Manager driver")
       - RCU/lockdep-splat.txt was added by commit d7bd2d68 ("rcu:
         Document interpretation of RCU-lockdep splats")
       - s390/kvm.txt was added by 5ecee4ba (KVM: s390: API documentation)
       - s390/qeth.txt was added by commit b4d72c08 ("qeth: bridgeport
         support - basic control")
       - scheduler/sched-bwc.txt was added by commit 88ebc08e ("sched: Add
         documentation for bandwidth control")
       - scsi/advansys.txt was added by commit 4bd6d7f3 ("[SCSI] advansys:
         Move documentation to Documentation/scsi")
       - scsi/bfa.txt was added by commit 1ec90174 ("[SCSI] bfa: add
         readme file")
       - scsi/bnx2fc.txt was added by commit 12b8fc10 ("[SCSI] bnx2fc: Add
         driver documentation")
       - scsi/cxgb3i.txt was added by commit c3673464 ("[SCSI] cxgb3i: Add
         cxgb3i iSCSI driver.")
       - scsi/hpsa.txt was added by commit 992ebcf1 ("[SCSI] hpsa: Add
         hpsa.txt to Documentation/scsi")
       - scsi/link_power_management_policy.txt was added by commit
         ca77329f ("[libata] Link power management infrastructure")
       - scsi/osd.txt was added by commit 78e0c621 ("[SCSI] osd:
         Documentation for OSD library")
       - scsi/scsi-parameter.txt was created/moved by commit 163475fb
         ("Documentation: move SCSI parameters to their own text file")
       - serial/driver was part of the initial repo
       - serial/n_gsm.txt was added by commit 323e8412 ("n_gsm: add a
       - timers/Makefile was added by commit 3794f3e8 ("docsrc: build
         Documentation/ sources")
       - virt/kvm/s390.txt was added by commit d9101fca ("KVM: s390:
         diagnose call documentation")
       - vm/split_page_table_lock was added by commit 49076ec2 ("mm:
         dynamically allocate page->ptl if it cannot be embedded to struct
       - w1/slaves/w1_ds28e04 was added by commit fbf7f7b4 ("w1: Add
         1-wire slave device driver for DS28E04-100")
       - w1/masters/omap-hdq was added by commit e0a29382 ("hdq:
         documentation for OMAP HDQ")
       - x86/early-microcode.txt was added by commit 0d91ea86 ("x86, doc:
         Documentation for early microcode loading")
       - x86/earlyprintk.txt was added by commit a1aade47 ("x86/doc:
         mini-howto for using earlyprintk=dbgp")
       - x86/entry_64.txt was added by commit 8b4777a4 ("x86-64: Document
         some of entry_64.S")
       - x86/pat.txt was added by commit d27554d8 ("x86: PAT
      Moved files
       - arm/kernel_user_helpers.txt was moved out of arch/arm/kernel by
         commit 37b83046 ("ARM: kuser: move interface documentation out of
         the source code")
       - efi-stub.txt was moved out of x86/ and down into Documentation/ in
         commit 4172fe2f ("EFI stub documentation updates")
       - laptops/hpfall.c was moved out of hwmon/ and into laptops/ in commit
         efcfed9b ("Move hp_accel to drivers/platform/x86")
       - commit 5616c23a ("x86: doc: move x86-generic documentation from
         * x86/usb-legacy-support.txt
         * x86/boot.txt
         * x86/zero_page.txt
       - power/video_extension.txt was moved to acpi in commit 70e66e4d
         ("ACPI / video: move video_extension.txt to Documentation/acpi")
      Removed files (left in 00-INDEX)
       - memory.txt was removed by commit 00ea8990 ("memory.txt: remove
         stray information")
       - gpio.txt was moved to gpio/ in commit fd8e198c ("Documentation:
         gpiolib: document new interface")
       - networking/DLINK.txt was removed by commit 168e06ae
         ("drivers/net: delete old parallel port de600/de620 drivers")
       - serial/hayes-esp.txt was removed by commit f53a2ade ("tty: esp:
         remove broken driver")
       - s390/TAPE was removed by commit 9e280f66 ("[S390] remove tape
         block docu")
       - vm/locking was removed by commit 57ea8171 ("mm: documentation:
         remove hopelessly out-of-date locking doc")
       - laptops/acer-wmi.txt was remvoed by commit 02003667 ("acer-wmi:
         Delete out-of-date documentation")
      Typos/misc issues
       - rpc-server-gss.txt was added as knfsd-rpcgss.txt in commit
         030d794b ("SUNRPC: Use gssproxy upcall for server RPCGSS
       - commit b88cf73d ("net: add missing entries to
         * generic-hdlc.txt was added as generic_hdlc.txt
         * spider_net.txt was added as spider-net.txt
       - w1/master/mxc-w1 was added as mxc_w1 by commit a5fd9139 ("w1: add
         1-wire master driver for i.MX27 / i.MX31")
       - s390/zfcpdump.txt was added as zfcpdump by commit 6920c12a
         ("[S390] Add Documentation/s390/00-INDEX.")
      Signed-off-by: default avatarHenrik Austad <henrik@austad.us>
      Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>	[rcu bits]
      Acked-by: default avatarRob Landley <rob@landley.net>
      Cc: Jiri Kosina <jkosina@suse.cz>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Rob Herring <robh+dt@kernel.org>
      Cc: David S. Miller <davem@davemloft.net>
      Cc: Mark Brown <broonie@kernel.org>
      Cc: "H. Peter Anvin" <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Gleb Natapov <gleb@kernel.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Len Brown <len.brown@intel.com>
      Cc: James Bottomley <JBottomley@parallels.com>
      Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  20. 03 Dec, 2013 2 commits
    • Paul E. McKenney's avatar
      rcu: Break call_rcu() deadlock involving scheduler and perf · 96d3fd0d
      Paul E. McKenney authored
      Dave Jones got the following lockdep splat:
      >  ======================================================
      >  [ INFO: possible circular locking dependency detected ]
      >  3.12.0-rc3+ #92 Not tainted
      >  -------------------------------------------------------
      >  trinity-child2/15191 is trying to acquire lock:
      >   (&rdp->nocb_wq){......}, at: [<ffffffff8108ff43>] __wake_up+0x23/0x50
      > but task is already holding lock:
      >   (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230
      > which lock already depends on the new lock.
      > the existing dependency chain (in reverse order) is:
      > -> #3 (&ctx->lock){-.-...}:
      >         [<ffffffff810cc243>] lock_acquire+0x93/0x200
      >         [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80
      >         [<ffffffff811500ff>] __perf_event_task_sched_out+0x2df/0x5e0
      >         [<ffffffff81091b83>] perf_event_task_sched_out+0x93/0xa0
      >         [<ffffffff81732052>] __schedule+0x1d2/0xa20
      >         [<ffffffff81732f30>] preempt_schedule_irq+0x50/0xb0
      >         [<ffffffff817352b6>] retint_kernel+0x26/0x30
      >         [<ffffffff813eed04>] tty_flip_buffer_push+0x34/0x50
      >         [<ffffffff813f0504>] pty_write+0x54/0x60
      >         [<ffffffff813e900d>] n_tty_write+0x32d/0x4e0
      >         [<ffffffff813e5838>] tty_write+0x158/0x2d0
      >         [<ffffffff811c4850>] vfs_write+0xc0/0x1f0
      >         [<ffffffff811c52cc>] SyS_write+0x4c/0xa0
      >         [<ffffffff8173d4e4>] tracesys+0xdd/0xe2
      > -> #2 (&rq->lock){-.-.-.}:
      >         [<ffffffff810cc243>] lock_acquire+0x93/0x200
      >         [<ffffffff81733f90>] _raw_spin_lock+0x40/0x80
      >         [<ffffffff810980b2>] wake_up_new_task+0xc2/0x2e0
      >         [<ffffffff81054336>] do_fork+0x126/0x460
      >         [<ffffffff81054696>] kernel_thread+0x26/0x30
      >         [<ffffffff8171ff93>] rest_init+0x23/0x140
      >         [<ffffffff81ee1e4b>] start_kernel+0x3f6/0x403
      >         [<ffffffff81ee1571>] x86_64_start_reservations+0x2a/0x2c
      >         [<ffffffff81ee1664>] x86_64_start_kernel+0xf1/0xf4
      > -> #1 (&p->pi_lock){-.-.-.}:
      >         [<ffffffff810cc243>] lock_acquire+0x93/0x200
      >         [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90
      >         [<ffffffff810979d1>] try_to_wake_up+0x31/0x350
      >         [<ffffffff81097d62>] default_wake_function+0x12/0x20
      >         [<ffffffff81084af8>] autoremove_wake_function+0x18/0x40
      >         [<ffffffff8108ea38>] __wake_up_common+0x58/0x90
      >         [<ffffffff8108ff59>] __wake_up+0x39/0x50
      >         [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0
      >         [<ffffffff81111450>] __call_rcu+0x140/0x820
      >         [<ffffffff81111b8d>] call_rcu+0x1d/0x20
      >         [<ffffffff81093697>] cpu_attach_domain+0x287/0x360
      >         [<ffffffff81099d7e>] build_sched_domains+0xe5e/0x10a0
      >         [<ffffffff81efa7fc>] sched_init_smp+0x3b7/0x47a
      >         [<ffffffff81ee1f4e>] kernel_init_freeable+0xf6/0x202
      >         [<ffffffff817200be>] kernel_init+0xe/0x190
      >         [<ffffffff8173d22c>] ret_from_fork+0x7c/0xb0
      > -> #0 (&rdp->nocb_wq){......}:
      >         [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0
      >         [<ffffffff810cc243>] lock_acquire+0x93/0x200
      >         [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90
      >         [<ffffffff8108ff43>] __wake_up+0x23/0x50
      >         [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0
      >         [<ffffffff81111450>] __call_rcu+0x140/0x820
      >         [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30
      >         [<ffffffff81149abf>] put_ctx+0x4f/0x70
      >         [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230
      >         [<ffffffff81056b8d>] do_exit+0x30d/0xcc0
      >         [<ffffffff8105893c>] do_group_exit+0x4c/0xc0
      >         [<ffffffff810589c4>] SyS_exit_group+0x14/0x20
      >         [<ffffffff8173d4e4>] tracesys+0xdd/0xe2
      > other info that might help us debug this:
      > Chain exists of:
      >   &rdp->nocb_wq --> &rq->lock --> &ctx->lock
      >   Possible unsafe locking scenario:
      >         CPU0                    CPU1
      >         ----                    ----
      >    lock(&ctx->lock);
      >                                 lock(&rq->lock);
      >                                 lock(&ctx->lock);
      >    lock(&rdp->nocb_wq);
      >  *** DEADLOCK ***
      > 1 lock held by trinity-child2/15191:
      >  #0:  (&ctx->lock){-.-...}, at: [<ffffffff81154c19>] perf_event_exit_task+0x109/0x230
      > stack backtrace:
      > CPU: 2 PID: 15191 Comm: trinity-child2 Not tainted 3.12.0-rc3+ #92
      >  ffffffff82565b70 ffff880070c2dbf8 ffffffff8172a363 ffffffff824edf40
      >  ffff880070c2dc38 ffffffff81726741 ffff880070c2dc90 ffff88022383b1c0
      >  ffff88022383aac0 0000000000000000 ffff88022383b188 ffff88022383b1c0
      > Call Trace:
      >  [<ffffffff8172a363>] dump_stack+0x4e/0x82
      >  [<ffffffff81726741>] print_circular_bug+0x200/0x20f
      >  [<ffffffff810cb7ca>] __lock_acquire+0x191a/0x1be0
      >  [<ffffffff810c6439>] ? get_lock_stats+0x19/0x60
      >  [<ffffffff8100b2f4>] ? native_sched_clock+0x24/0x80
      >  [<ffffffff810cc243>] lock_acquire+0x93/0x200
      >  [<ffffffff8108ff43>] ? __wake_up+0x23/0x50
      >  [<ffffffff8173419b>] _raw_spin_lock_irqsave+0x4b/0x90
      >  [<ffffffff8108ff43>] ? __wake_up+0x23/0x50
      >  [<ffffffff8108ff43>] __wake_up+0x23/0x50
      >  [<ffffffff8110d4f8>] __call_rcu_nocb_enqueue+0xa8/0xc0
      >  [<ffffffff81111450>] __call_rcu+0x140/0x820
      >  [<ffffffff8109bc8f>] ? local_clock+0x3f/0x50
      >  [<ffffffff81111bb0>] kfree_call_rcu+0x20/0x30
      >  [<ffffffff81149abf>] put_ctx+0x4f/0x70
      >  [<ffffffff81154c3e>] perf_event_exit_task+0x12e/0x230
      >  [<ffffffff81056b8d>] do_exit+0x30d/0xcc0
      >  [<ffffffff810c9af5>] ? trace_hardirqs_on_caller+0x115/0x1e0
      >  [<ffffffff810c9bcd>] ? trace_hardirqs_on+0xd/0x10
      >  [<ffffffff8105893c>] do_group_exit+0x4c/0xc0
      >  [<ffffffff810589c4>] SyS_exit_group+0x14/0x20
      >  [<ffffffff8173d4e4>] tracesys+0xdd/0xe2
      The underlying problem is that perf is invoking call_rcu() with the
      scheduler locks held, but in NOCB mode, call_rcu() will with high
      probability invoke the scheduler -- which just might want to use its
      locks.  The reason that call_rcu() needs to invoke the scheduler is
      to wake up the corresponding rcuo callback-offload kthread, which
      does the job of starting up a grace period and invoking the callbacks
      One solution (championed on a related problem by Lai Jiangshan) is to
      simply defer the wakeup to some point where scheduler locks are no longer
      held.  Since we don't want to unnecessarily incur the cost of such
      deferral, the task before us is threefold:
      1.	Determine when it is likely that a relevant scheduler lock is held.
      2.	Defer the wakeup in such cases.
      3.	Ensure that all deferred wakeups eventually happen, preferably
      	sooner rather than later.
      We use irqs_disabled_flags() as a proxy for relevant scheduler locks
      being held.  This works because the relevant locks are always acquired
      with interrupts disabled.  We may defer more often than needed, but that
      is at least safe.
      The wakeup deferral is tracked via a new field in the per-CPU and
      per-RCU-flavor rcu_data structure, namely ->nocb_defer_wakeup.
      This flag is checked by the RCU core processing.  The __rcu_pending()
      function now checks this flag, which causes rcu_check_callbacks()
      to initiate RCU core processing at each scheduling-clock interrupt
      where this flag is set.  Of course this is not sufficient because
      scheduling-clock interrupts are often turned off (the things we used to
      be able to count on!).  So the flags are also checked on entry to any
      state that RCU considers to be idle, which includes both NO_HZ_IDLE idle
      state and NO_HZ_FULL user-mode-execution state.
      This approach should allow call_rcu() to be invoked regardless of what
      locks you might be holding, the key word being "should".
      Reported-by: default avatarDave Jones <davej@redhat.com>
      Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
    • Paul E. McKenney's avatar
  21. 25 Sep, 2013 1 commit