• Darrick J. Wong's avatar
    xfs: periodically yield scrub threads to the scheduler · 5d1116d4
    Darrick J. Wong authored
    Christoph Hellwig complained about the following soft lockup warning
    when running scrub after generic/175 when preemption is disabled and
    slub debugging is enabled:
    
    watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [xfs_scrub:161]
    Modules linked in:
    irq event stamp: 41692326
    hardirqs last  enabled at (41692325): [<ffffffff8232c3b7>] _raw_0
    hardirqs last disabled at (41692326): [<ffffffff81001c5a>] trace0
    softirqs last  enabled at (41684994): [<ffffffff8260031f>] __do_e
    softirqs last disabled at (41684987): [<ffffffff81127d8c>] irq_e0
    CPU: 3 PID: 16189 Comm: xfs_scrub Not tainted 5.4.0-rc3+ #30
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.124
    RIP: 0010:_raw_spin_unlock_irqrestore+0x39/0x40
    Code: 89 f3 be 01 00 00 00 e8 d5 3a e5 fe 48 89 ef e8 ed 87 e5 f2
    RSP: 0018:ffffc9000233f970 EFLAGS: 00000286 ORIG_RAX: ffffffffff3
    RAX: ffff88813b398040 RBX: 0000000000000286 RCX: 0000000000000006
    RDX: 0000000000000006 RSI: ffff88813b3988c0 RDI: ffff88813b398040
    RBP: ffff888137958640 R08: 0000000000000001 R09: 0000000000000000
    R10: 0000000000000000 R11: 0000000000000000 R12: ffffea00042b0c00
    R13: 0000000000000001 R14: ffff88810ac32308 R15: ffff8881376fc040
    FS:  00007f6113dea700(0000) GS:ffff88813bb80000(0000) knlGS:00000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f6113de8ff8 CR3: 000000012f290000 CR4: 00000000000006e0
    Call Trace:
     free_debug_processing+0x1dd/0x240
     __slab_free+0x231/0x410
     kmem_cache_free+0x30e/0x360
     xchk_ag_btcur_free+0x76/0xb0
     xchk_ag_free+0x10/0x80
     xchk_bmap_iextent_xref.isra.14+0xd9/0x120
     xchk_bmap_iextent+0x187/0x210
     xchk_bmap+0x2e0/0x3b0
     xfs_scrub_metadata+0x2e7/0x500
     xfs_ioc_scrub_metadata+0x4a/0xa0
     xfs_file_ioctl+0x58a/0xcd0
     do_vfs_ioctl+0xa0/0x6f0
     ksys_ioctl+0x5b/0x90
     __x64_sys_ioctl+0x11/0x20
     do_syscall_64+0x4b/0x1a0
     entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
    If preemption is disabled, all metadata buffers needed to perform the
    scrub are already in memory, and there are a lot of records to check,
    it's possible that the scrub thread will run for an extended period of
    time without sleeping for IO or any other reason.  Then the watchdog
    timer or the RCU stall timeout can trigger, producing the backtrace
    above.
    
    To fix this problem, call cond_resched() from the scrub thread so that
    we back out to the scheduler whenever necessary.
    Reported-by: default avatarChristoph Hellwig <hch@infradead.org>
    Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    5d1116d4
common.h 5.07 KB