On Thu, Sep 21, 2017 at 03:22:34PM +0530, Chandan Rajendra wrote: > Executing xfs/104 test in a loop on Linux-v4.13 kernel on a ppc64 > machine can cause the following NULL pointer dereference, > > Unable to handle kernel paging request for data at address 0x00000100 > Faulting instruction address: 0xc0000000000fece8 > Oops: Kernel access of bad area, sig: 11 [#1] > SMP NR_CPUS=2048 > DEBUG_PAGEALLOC > NUMA > pSeries > Modules linked in: > CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.13.0 #1 > task: c00000063849c200 task.stack: c0000006384f0000 > NIP: c0000000000fece8 LR: c0000000000ff2cc CTR: c000000000383380 > REGS: c00000063ffdb400 TRAP: 0300 Not tainted (4.13.0) > MSR: 8000000000009032 <SF,EE,ME,IR,DR,RI> > CR: 28002222 XER: 20000000 > CFAR: c0000000000227a4 DAR: 0000000000000100 DSISR: 40000000 SOFTE: 0 > GPR00: c0000000000ff2cc c00000063ffdb680 c000000001252e00 0000000000000800 > GPR04: 0000000000000000 c0000006387b8730 c000000633d5db70 0000000fffffffe1 > GPR08: c0000003aa89ed68 0000000000000000 0000000000000000 c000000633d5db70 > GPR12: 0000000028002422 c00000000fd80a00 c0000006384f3f90 c00000063ffd8000 > GPR16: 0000000000000000 c0000006387b8730 c0000000012475e0 c0000000012475e0 > GPR20: 0000000000000002 0000000000000000 0000000000000001 0000000000000002 > GPR24: 0000000000000010 c00000063e155800 0000000000000800 0000000000000800 > GPR28: 0000000000000000 c000000633d5db00 0000000000000000 0000000000000000 > NIP [c0000000000fece8] .__queue_work+0x68/0x600 > LR [c0000000000ff2cc] .queue_work_on+0x4c/0x80 > Call Trace: > [c00000063ffdb680] [c00000063ffdb720] 0xc00000063ffdb720 (unreliable) > [c00000063ffdb770] [c0000000000ff2cc] .queue_work_on+0x4c/0x80 > [c00000063ffdb7f0] [c00000000038343c] .iomap_dio_bio_end_io+0xbc/0x1f0 > [c00000063ffdb880] [c0000000006cdc18] .bio_endio+0x118/0x1f0 > [c00000063ffdb910] [c0000000006d9e30] .blk_update_request+0xd0/0x470 > [c00000063ffdb9b0] [c0000000006e8284] .blk_mq_end_request+0x24/0xc0 > [c00000063ffdba30] [c00000000082ba50] .lo_complete_rq+0x40/0xe0 > [c00000063ffdbab0] [c0000000006e5e48] .__blk_mq_complete_request_remote+0x28/0x40 > [c00000063ffdbb20] [c00000000018e674] .flush_smp_call_function_queue+0xc4/0x1e0 > [c00000063ffdbbb0] [c00000000003f94c] .smp_ipi_demux_relaxed+0x8c/0x100 > [c00000063ffdbc40] [c000000000081054] .icp_hv_ipi_action+0x54/0xa0 > [c00000063ffdbcc0] [c0000000001505a4] .__handle_irq_event_percpu+0x84/0x2c0 > [c00000063ffdbd90] [c000000000150808] .handle_irq_event_percpu+0x28/0x80 > [c00000063ffdbe20] [c000000000156858] .handle_percpu_irq+0x78/0xc0 > [c00000063ffdbea0] [c00000000014ee70] .generic_handle_irq+0x40/0x70 > [c00000063ffdbf10] [c000000000015a88] .__do_irq+0x88/0x200 > [c00000063ffdbf90] [c000000000027a70] .call_do_irq+0x14/0x24 > [c0000006384f3810] [c000000000015c84] .do_IRQ+0x84/0x130 > > This occurs due to the following sequence of events, > > 1. Allocate dio for Direct I/O write. > 2. Invoke iomap_apply() until iov_iter_count() bytes have been submitted. > - Assume that we have submitted atleast one bio. Hence iomap_dio->ref value > will be >= 2. > - If during the second iteration, iomap_apply() ends up returning -ENOSPC, we would > break out of the loop and since the 'ret' value is a negative number we > end up not allocating memory for super_block->s_dio_done_wq. > 3. Meanwhile, iomap_dio_bio_end_io() is invoked for bios that have been > submitted and here the code ends up dereferencing the NULL pointer stored > at super_block->s_dio_done_wq. > > This commit fixes the bug by allocating memory for > super_block->s_dio_done_wq before iomap_apply() is invoked. > > Reported-by: Eryu Guan <eguan@xxxxxxxxxx> > Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx> I tested this patch on x86_64 host. Without the patch, I could crash the host by running xfs/104 within 50 iterations, and host survived 500 iterations of xfs/104 run with this patch applied. So Tested-by: Eryu Guan <eguan@xxxxxxxxxx> Thanks! Eryu -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
