1. 07 Oct, 2016 3 commits
    • zhong jiang's avatar
      mm,ksm: fix endless looping in allocating memory when ksm enable · a2fc10c3
      zhong jiang authored
      commit 5b398e41 upstream.
      
      I hit the following hung task when runing a OOM LTP test case with 4.1
      kernel.
      
      Call trace:
      [<ffffffc000086a88>] __switch_to+0x74/0x8c
      [<ffffffc000a1bae0>] __schedule+0x23c/0x7bc
      [<ffffffc000a1c09c>] schedule+0x3c/0x94
      [<ffffffc000a1eb84>] rwsem_down_write_failed+0x214/0x350
      [<ffffffc000a1e32c>] down_write+0x64/0x80
      [<ffffffc00021f794>] __ksm_exit+0x90/0x19c
      [<ffffffc0000be650>] mmput+0x118/0x11c
      [<ffffffc0000c3ec4>] do_exit+0x2dc/0xa74
      [<ffffffc0000c46f8>] do_group_exit+0x4c/0xe4
      [<ffffffc0000d0f34>] get_signal+0x444/0x5e0
      [<ffffffc000089fcc>] do_signal+0x1d8/0x450
      [<ffffffc00008a35c>] do_notify_resume+0x70/0x78
      
      The oom victim cannot terminate because it needs to take mmap_sem for
      write while the lock is held by ksmd for read which loops in the page
      allocator
      
      ksm_do_scan
      	scan_get_next_rmap_item
      		down_read
      		get_next_rmap_item
      			alloc_rmap_item   #ksmd will loop permanently.
      
      There is no way forward because the oom victim cannot release any memory
      in 4.1 based kernel.  Since 4.6 we have the oom reaper which would solve
      this problem because it would release the memory asynchronously.
      Nevertheless we can relax alloc_rmap_item requirements and use
      __GFP_NORETRY because the allocation failure is acceptable as ksm_do_scan
      would just retry later after the lock got dropped.
      
      Such a patch would be also easy to backport to older stable kernels which
      do not have oom_reaper.
      
      While we are at it add GFP_NOWARN so the admin doesn't have to be alarmed
      by the allocation failure.
      
      Link: http://lkml.kernel.org/r/1474165570-44398-1-git-send-email-zhongjiang@huawei.comSigned-off-by: default avatarzhong jiang <zhongjiang@huawei.com>
      Suggested-by: default avatarHugh Dickins <hughd@google.com>
      Suggested-by: default avatarMichal Hocko <mhocko@suse.cz>
      Acked-by: default avatarMichal Hocko <mhocko@suse.com>
      Acked-by: default avatarHugh Dickins <hughd@google.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      a2fc10c3
    • Karl Beldan's avatar
      mtd: nand: davinci: Reinitialize the HW ECC engine in 4bit hwctl · 05d721d6
      Karl Beldan authored
      commit f6d7c1b5 upstream.
      
      This fixes subpage writes when using 4-bit HW ECC.
      
      There has been numerous reports about ECC errors with devices using this
      driver for a while.  Also the 4-bit ECC has been reported as broken with
      subpages in [1] and with 16 bits NANDs in the driver and in mach* board
      files both in mainline and in the vendor BSPs.
      
      What I saw with 4-bit ECC on a 16bits NAND (on an LCDK) which got me to
      try reinitializing the ECC engine:
      - R/W on whole pages properly generates/checks RS code
      - try writing the 1st subpage only of a blank page, the subpage is well
        written and the RS code properly generated, re-reading the same page
        the HW detects some ECC error, reading the same page again no ECC
        error is detected
      
      Note that the ECC engine is already reinitialized in the 1-bit case.
      
      Tested on my LCDK with UBI+UBIFS using subpages.
      This could potentially get rid of the issue workarounded in [1].
      
      [1] 28c015a9 ("mtd: davinci-nand: disable subpage write for keystone-nand")
      
      Fixes: 6a4123e5 ("mtd: nand: davinci_nand, 4-bit ECC for smallpage")
      Signed-off-by: default avatarKarl Beldan <kbeldan@baylibre.com>
      Acked-by: default avatarBoris Brezillon <boris.brezillon@free-electrons.com>
      Signed-off-by: default avatarBrian Norris <computersforpeace@gmail.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      05d721d6
    • Joonwoo Park's avatar
      cpuset: handle race between CPU hotplug and cpuset_hotplug_work · 8132ffc9
      Joonwoo Park authored
      commit 28b89b9e upstream.
      
      A discrepancy between cpu_online_mask and cpuset's effective_cpus
      mask is inevitable during hotplug since cpuset defers updating of
      effective_cpus mask using a workqueue, during which time nothing
      prevents the system from more hotplug operations.  For that reason
      guarantee_online_cpus() walks up the cpuset hierarchy until it finds
      an intersection under the assumption that top cpuset's effective_cpus
      mask intersects with cpu_online_mask even with such a race occurring.
      
      However a sequence of CPU hotplugs can open a time window, during which
      none of the effective CPUs in the top cpuset intersect with
      cpu_online_mask.
      
      For example when there are 4 possible CPUs 0-3 and only CPU0 is online:
      
        ========================  ===========================
         cpu_online_mask           top_cpuset.effective_cpus
        ========================  ===========================
         echo 1 > cpu2/online.
         CPU hotplug notifier woke up hotplug work but not yet scheduled.
            [0,2]                     [0]
      
         echo 0 > cpu0/online.
         The workqueue is still runnable.
            [2]                       [0]
        ========================  ===========================
      
        Now there is no intersection between cpu_online_mask and
        top_cpuset.effective_cpus.  Thus invoking sys_sched_setaffinity() at
        this moment can cause following:
      
         Unable to handle kernel NULL pointer dereference at virtual address 000000d0
         ------------[ cut here ]------------
         Kernel BUG at ffffffc0001389b0 [verbose debug info unavailable]
         Internal error: Oops - BUG: 96000005 [#1] PREEMPT SMP
         Modules linked in:
         CPU: 2 PID: 1420 Comm: taskset Tainted: G        W       4.4.8+ #98
         task: ffffffc06a5c4880 ti: ffffffc06e124000 task.ti: ffffffc06e124000
         PC is at guarantee_online_cpus+0x2c/0x58
         LR is at cpuset_cpus_allowed+0x4c/0x6c
         <snip>
         Process taskset (pid: 1420, stack limit = 0xffffffc06e124020)
         Call trace:
         [<ffffffc0001389b0>] guarantee_online_cpus+0x2c/0x58
         [<ffffffc00013b208>] cpuset_cpus_allowed+0x4c/0x6c
         [<ffffffc0000d61f0>] sched_setaffinity+0xc0/0x1ac
         [<ffffffc0000d6374>] SyS_sched_setaffinity+0x98/0xac
         [<ffffffc000085cb0>] el0_svc_naked+0x24/0x28
      
      The top cpuset's effective_cpus are guaranteed to be identical to
      cpu_online_mask eventually.  Hence fall back to cpu_online_mask when
      there is no intersection between top cpuset's effective_cpus and
      cpu_online_mask.
      Signed-off-by: default avatarJoonwoo Park <joonwoop@codeaurora.org>
      Acked-by: default avatarLi Zefan <lizefan@huawei.com>
      Cc: Tejun Heo <tj@kernel.org>
      Cc: cgroups@vger.kernel.org
      Cc: linux-kernel@vger.kernel.org
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      8132ffc9
  2. 30 Sep, 2016 37 commits