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    Subject[PATCH 4.4 05/64] btrfs: reschedule when cloning lots of extents
    Date
    From: Johannes Thumshirn <johannes.thumshirn@wdc.com>

    [ Upstream commit 6b613cc97f0ace77f92f7bc112b8f6ad3f52baf8 ]

    We have several occurrences of a soft lockup from fstest's generic/175
    testcase, which look more or less like this one:

    watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [xfs_io:10030]
    Kernel panic - not syncing: softlockup: hung tasks
    CPU: 0 PID: 10030 Comm: xfs_io Tainted: G L 5.9.0-rc5+ #768
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4-rebuilt.opensuse.org 04/01/2014
    Call Trace:
    <IRQ>
    dump_stack+0x77/0xa0
    panic+0xfa/0x2cb
    watchdog_timer_fn.cold+0x85/0xa5
    ? lockup_detector_update_enable+0x50/0x50
    __hrtimer_run_queues+0x99/0x4c0
    ? recalibrate_cpu_khz+0x10/0x10
    hrtimer_run_queues+0x9f/0xb0
    update_process_times+0x28/0x80
    tick_handle_periodic+0x1b/0x60
    __sysvec_apic_timer_interrupt+0x76/0x210
    asm_call_on_stack+0x12/0x20
    </IRQ>
    sysvec_apic_timer_interrupt+0x7f/0x90
    asm_sysvec_apic_timer_interrupt+0x12/0x20
    RIP: 0010:btrfs_tree_unlock+0x91/0x1a0 [btrfs]
    RSP: 0018:ffffc90007123a58 EFLAGS: 00000282
    RAX: ffff8881cea2fbe0 RBX: ffff8881cea2fbe0 RCX: 0000000000000000
    RDX: ffff8881d23fd200 RSI: ffffffff82045220 RDI: ffff8881cea2fba0
    RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000032
    R10: 0000160000000000 R11: 0000000000001000 R12: 0000000000001000
    R13: ffff8882357fd5b0 R14: ffff88816fa76e70 R15: ffff8881cea2fad0
    ? btrfs_tree_unlock+0x15b/0x1a0 [btrfs]
    btrfs_release_path+0x67/0x80 [btrfs]
    btrfs_insert_replace_extent+0x177/0x2c0 [btrfs]
    btrfs_replace_file_extents+0x472/0x7c0 [btrfs]
    btrfs_clone+0x9ba/0xbd0 [btrfs]
    btrfs_clone_files.isra.0+0xeb/0x140 [btrfs]
    ? file_update_time+0xcd/0x120
    btrfs_remap_file_range+0x322/0x3b0 [btrfs]
    do_clone_file_range+0xb7/0x1e0
    vfs_clone_file_range+0x30/0xa0
    ioctl_file_clone+0x8a/0xc0
    do_vfs_ioctl+0x5b2/0x6f0
    __x64_sys_ioctl+0x37/0xa0
    do_syscall_64+0x33/0x40
    entry_SYSCALL_64_after_hwframe+0x44/0xa9
    RIP: 0033:0x7f87977fc247
    RSP: 002b:00007ffd51a2f6d8 EFLAGS: 00000206 ORIG_RAX: 0000000000000010
    RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f87977fc247
    RDX: 00007ffd51a2f710 RSI: 000000004020940d RDI: 0000000000000003
    RBP: 0000000000000004 R08: 00007ffd51a79080 R09: 0000000000000000
    R10: 00005621f11352f2 R11: 0000000000000206 R12: 0000000000000000
    R13: 0000000000000000 R14: 00005621f128b958 R15: 0000000080000000
    Kernel Offset: disabled
    ---[ end Kernel panic - not syncing: softlockup: hung tasks ]---

    All of these lockup reports have the call chain btrfs_clone_files() ->
    btrfs_clone() in common. btrfs_clone_files() calls btrfs_clone() with
    both source and destination extents locked and loops over the source
    extent to create the clones.

    Conditionally reschedule in the btrfs_clone() loop, to give some time back
    to other processes.

    CC: stable@vger.kernel.org # 4.4+
    Reviewed-by: Josef Bacik <josef@toxicpanda.com>
    Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/btrfs/ioctl.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
    index 67366515a29d2..f35e18e76f160 100644
    --- a/fs/btrfs/ioctl.c
    +++ b/fs/btrfs/ioctl.c
    @@ -3856,6 +3856,8 @@ process_slot:
    ret = -EINTR;
    goto out;
    }
    +
    + cond_resched();
    }
    ret = 0;

    --
    2.27.0


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