• Michal Hocko's avatar
    mm: limit mmu_gather batching to fix soft lockups on !CONFIG_PREEMPT · 53a59fc6
    Michal Hocko authored
    Since commit e303297e ("mm: extended batches for generic
    mmu_gather") we are batching pages to be freed until either
    tlb_next_batch cannot allocate a new batch or we are done.
    
    This works just fine most of the time but we can get in troubles with
    non-preemptible kernel (CONFIG_PREEMPT_NONE or CONFIG_PREEMPT_VOLUNTARY)
    on large machines where too aggressive batching might lead to soft
    lockups during process exit path (exit_mmap) because there are no
    scheduling points down the free_pages_and_swap_cache path and so the
    freeing can take long enough to trigger the soft lockup.
    
    The lockup is harmless except when the system is setup to panic on
    softlockup which is not that unusual.
    
    The simplest way to work around this issue is to limit the maximum
    number of batches in a single mmu_gather.  10k of collected pages should
    be safe to prevent from soft lockups (we would have 2ms for one) even if
    they are all freed without an explicit scheduling point.
    
    This patch doesn't add any new explicit scheduling points because it
    relies on zap_pmd_range during page tables zapping which calls
    cond_resched per PMD.
    
    The following lockup has been reported for 3.0 kernel with a huge
    process (in order of hundreds gigs but I do know any more details).
    
      BUG: soft lockup - CPU#56 stuck for 22s! [kernel:31053]
      Modules linked in: af_packet nfs lockd fscache auth_rpcgss nfs_acl sunrpc mptctl mptbase autofs4 binfmt_misc dm_round_robin dm_multipath bonding cpufreq_conservative cpufreq_userspace cpufreq_powersave pcc_cpufreq mperf microcode fuse loop osst sg sd_mod crc_t10dif st qla2xxx scsi_transport_fc scsi_tgt netxen_nic i7core_edac iTCO_wdt joydev e1000e serio_raw pcspkr edac_core iTCO_vendor_support acpi_power_meter rtc_cmos hpwdt hpilo button container usbhid hid dm_mirror dm_region_hash dm_log linear uhci_hcd ehci_hcd usbcore usb_common scsi_dh_emc scsi_dh_alua scsi_dh_hp_sw scsi_dh_rdac scsi_dh dm_snapshot pcnet32 mii edd dm_mod raid1 ext3 mbcache jbd fan thermal processor thermal_sys hwmon cciss scsi_mod
      Supported: Yes
      CPU 56
      Pid: 31053, comm: kernel Not tainted 3.0.31-0.9-default #1 HP ProLiant DL580 G7
      RIP: 0010:  _raw_spin_unlock_irqrestore+0x8/0x10
      RSP: 0018:ffff883ec1037af0  EFLAGS: 00000206
      RAX: 0000000000000e00 RBX: ffffea01a0817e28 RCX: ffff88803ffd9e80
      RDX: 0000000000000200 RSI: 0000000000000206 RDI: 0000000000000206
      RBP: 0000000000000002 R08: 0000000000000001 R09: ffff887ec724a400
      R10: 0000000000000000 R11: dead000000200200 R12: ffffffff8144c26e
      R13: 0000000000000030 R14: 0000000000000297 R15: 000000000000000e
      FS:  00007ed834282700(0000) GS:ffff88c03f200000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      CR2: 000000000068b240 CR3: 0000003ec13c5000 CR4: 00000000000006e0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
      Process kernel (pid: 31053, threadinfo ffff883ec1036000, task ffff883ebd5d4100)
      Call Trace:
        release_pages+0xc5/0x260
        free_pages_and_swap_cache+0x9d/0xc0
        tlb_flush_mmu+0x5c/0x80
        tlb_finish_mmu+0xe/0x50
        exit_mmap+0xbd/0x120
        mmput+0x49/0x120
        exit_mm+0x122/0x160
        do_exit+0x17a/0x430
        do_group_exit+0x3d/0xb0
        get_signal_to_deliver+0x247/0x480
        do_signal+0x71/0x1b0
        do_notify_resume+0x98/0xb0
        int_signal+0x12/0x17
      DWARF2 unwinder stuck at int_signal+0x12/0x17
    Signed-off-by: default avatarMichal Hocko <mhocko@suse.cz>
    Cc: <stable@vger.kernel.org>	[3.0+]
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    53a59fc6
tlb.h 5.56 KB