On Thu, Jun 30, 2016 at 10:50:44AM +0200, Dmitry Vyukov wrote: > Hello, > > The following program triggers GPF in get_task_ioprio if run in a parallel loop: Dmitry, Could you please try the below? diff --git a/block/ioprio.c b/block/ioprio.c index cc7800e9eb44..01b8116298a1 100644 --- a/block/ioprio.c +++ b/block/ioprio.c @@ -150,8 +150,10 @@ static int get_task_ioprio(struct task_struct *p) if (ret) goto out; ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM); + task_lock(p); if (p->io_context) ret = p->io_context->ioprio; + task_unlock(p); out: return ret; } I'm having a hard time reproducing it but I can see how it could happen; I think `p->io_context` is getting freed in exit_io_context() in between the `if (p->io_context)` and `ret = p->io_context->ioprio`. Thanks, Omar > > // autogenerated by syzkaller (http://github.com/google/syzkaller) > #include <stdint.h> > #include <string.h> > #include <sys/syscall.h> > #include <unistd.h> > > int main() > { > syscall(SYS_ioprio_set, 0x2ul, 0x0ul, 0x7ffful, 0, 0, 0); > syscall(SYS_ioprio_get, 0x3ul, 0x0ul, 0, 0, 0, 0); > return 0; > } > > This patch also seems to help to trigger it: > > int set_task_ioprio(struct task_struct *task, int ioprio) > { > @@ -150,8 +151,10 @@ static int get_task_ioprio(struct task_struct *p) > if (ret) > goto out; > ret = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, IOPRIO_NORM); > - if (p->io_context) > + if (p->io_context) { > + ndelay(10000); > ret = p->io_context->ioprio; > + } > out: > return ret; > } > > kasan: GPF could be caused by NULL-ptr deref or user memory access > general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN > Modules linked in: > CPU: 2 PID: 8978 Comm: a.out Not tainted 4.7.0-rc5+ #22 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > task: ffff8800612397c0 ti: ffff880062d08000 task.ti: ffff880062d08000 > RIP: 0010:[<ffffffff82c7fa2a>] > [<ffffffff82c7fa2a>] get_task_ioprio+0x9a/0xe0 block/ioprio.c:156 > RSP: 0018:ffff880062d0feb8 EFLAGS: 00010206 > RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000007605 > RDX: 0000000000000009 RSI: 0000002004a58c71 RDI: 0000000000000048 > RBP: ffff880062d0fed0 R08: 0000000000000002 R09: 0000000000000002 > R10: 0000000000000000 R11: 0000000000000001 R12: ffff8800647817c0 > R13: ffff8800647827b0 R14: ffffffff82c80ac2 R15: dffffc0000000000 > FS: 0000000001127880(0000) GS:ffff88006d400000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00000000004b20c0 CR3: 0000000061894000 CR4: 00000000000006e0 > Stack: > ffff8800647817c0 0000000000000000 ffffffff8813a660 ffff880062d0ff48 > ffffffff82c80ec5 ffffffff82c80ac2 ffffffff880f8240 0000000362d0ff48 > 0000000000000000 000040037fff4003 fffffbfff101f048 ffffffff880f81e0 > Call Trace: > [< inline >] SYSC_ioprio_get block/ioprio.c:230 > [<ffffffff82c80ec5>] SyS_ioprio_get+0x795/0x9c0 block/ioprio.c:182 > [<ffffffff86a9b380>] entry_SYSCALL_64_fastpath+0x23/0xc1 > arch/x86/entry/entry_64.S:207 > Code: 00 fc ff df 48 c1 ea 03 80 3c 02 00 75 4f 49 8b 9c 24 f0 0f 00 > 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 48 48 89 fa 48 c1 ea 03 <0f> > b6 04 02 84 c0 74 04 3c 01 7e 12 0f b7 5b 48 e8 51 6f 91 fe > RIP [<ffffffff82c7fa2a>] get_task_ioprio+0x9a/0xe0 block/ioprio.c:156 > RSP <ffff880062d0feb8> > ---[ end trace 8b400ca760ff21a5 ]--- > > On commit 00bf377d19ad3d80cbc7a036521279a86e397bfb (Jun 29). > -- > To unsubscribe from this list: send the line "unsubscribe linux-block" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Omar -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
