Re: general protection fault (btrfs_real_readdir)

From: Markus Trippelsdorf
Date: Wed May 18 2016 - 09:02:14 EST


On 2016.05.18 at 13:21 +0100, Al Viro wrote:
> On Wed, May 18, 2016 at 01:31:40PM +0200, Markus Trippelsdorf wrote:
> > I'm running the latest Linus git tree and the parallel filesystem directory
> > handling update seems to cause the following issue:
>
> > Call Trace:
> > [<ffffffff812f038b>] ? btrfs_real_readdir+0x44b/0x540
> > [<ffffffff811b064d>] ? SyS_getdents+0x12d/0x2a0
> > [<ffffffff811affa0>] ? SyS_ioctl+0x6a0/0x6a0
> > [<ffffffff810923db>] ? entry_SYSCALL_64_fastpath+0x13/0x8f
> > Code: 02 00 00 00 00 ad de eb 1e f0 ff 4b 60 74 73 49 8b 47 40 49 8d 57 40 4c 89 fb 48 39 d5 4c 8d 78 c0 0f 84 8d 00 00 00 48 8b 53 48 <48> 89 50 08 48 89 02 4c 89 6b 40 4c 89 63 48 48 8b 4b 21 49 3b
> > RIP [<ffffffff8134e9f3>] btrfs_readdir_delayed_dir_index+0x73/0x120
> > RSP <ffff8801076e3dc0>
> > ---[ end trace 91067801e8a68a7e ]---
> >
> > This happened while I was building gcc, so the system was very busy.
>
> From a very superficial reading of delayed-inode.c, it looks like delayed
> node might need locking... This
> list_for_each_entry_safe(curr, next, ins_list, readdir_list) {
> list_del(&curr->readdir_list);
> looks particularly unpleasant. Just to make sure that this *is* just a
> readdir issue (and not something involving lookups), could you try to
> reproduce the breakage with 972b241f8 reverted?

For what it's worth, gcc bootstrapped fine with 972b241f8 reverted.

--
Markus