On Mon, 17 Dec 2007 14:56:44 PST, Andrew Morton said: (Adding Al Viro to the list, he's listed as "file systems" and MAINTAINERS doesn't list 'isofs' anyplace. Will Al or Andrew please vector to whoever actually does that code?)
> > I try it again, and it reports it died at the same exact place, but in about
> > 2 seconds flat, and reports 91M/sec transfer. OK, that's *weird*, I didn't
> > think that blocks read from /dev/cdrom would get cached, but OK.
>
> It'll remain cached if something is holding the device open.
Does it need to be "device open", or are there other things as well? If the
drop_cache was hosed, that would result in the same symptoms, no?
> Something's holding s_umount for writing I guess. Possibly busted error
> handling somewhere totally different.
Aha - found what was holding it - an attempt to loopback mount the truncated
file (before I realized it was truncated) had failed - I had gotten a 'Killed'
back from the mount, but I didn't realize it had pulled an actual oops:
Dec 17 15:54:33 turing-police kernel: [14503.402385] attempt to access beyond
end of device
Dec 17 15:54:33 turing-police kernel: [14503.402391] loop1: rw=0, want=1284500,
limit=314240
Dec 17 15:54:33 turing-police kernel: [14503.402395] ISOFS: unable to read
i-node block
Dec 17 15:54:33 turing-police kernel: [14503.402428] Unable to handle kernel
NULL pointer dereference at 000000000000010b RIP:
Dec 17 15:54:33 turing-police kernel: [14503.402440] [<ffffffff802a096b>]
iput+0x11/0x80
...
Dec 17 15:54:33 turing-police kernel: [14503.403008] Call Trace:
Dec 17 15:54:33 turing-police kernel: [14503.403026] [<ffffffff802ff73e>]
isofs_fill_super+0x7e9/0xa6b
Dec 17 15:54:33 turing-police kernel: [14503.403045] [<ffffffff80523d28>]
__down_write_nested+0x3d/0xa1
Dec 17 15:54:33 turing-police kernel: [14503.403061] [<ffffffff80523d97>]
__down_write+0xb/0xd
Dec 17 15:54:33 turing-police kernel: [14503.403076] [<ffffffff8028fb63>]
sget+0x397/0x3a9
Dec 17 15:54:33 turing-police kernel: [14503.403090] [<ffffffff8028f204>]
set_bdev_super+0x0/0x14
Dec 17 15:54:33 turing-police kernel: [14503.403106] [<ffffffff80290301>]
get_sb_bdev+0x109/0x157
Dec 17 15:54:33 turing-police kernel: [14503.403120] [<ffffffff802fef55>]
isofs_fill_super+0x0/0xa6b
Dec 17 15:54:33 turing-police kernel: [14503.403138] [<ffffffff802fe2e9>]
isofs_get_sb+0x13/0x15
Dec 17 15:54:33 turing-police kernel: [14503.403151] [<ffffffff80290075>]
vfs_kern_mount+0x90/0x11a
Dec 17 15:54:33 turing-police kernel: [14503.403167] [<ffffffff8029015c>]
do_kern_mount+0x47/0xe3
Dec 17 15:54:33 turing-police kernel: [14503.403183] [<ffffffff802a5012>]
do_mount+0x717/0x78a
Dec 17 15:54:33 turing-police kernel: [14503.403199] [<ffffffff805242fc>]
_read_lock_irq+0x9/0xb
Dec 17 15:54:33 turing-police kernel: [14503.403212] [<ffffffff8026cce0>]
find_lock_page+0x8c/0x97
Dec 17 15:54:33 turing-police kernel: [14503.403227] [<ffffffff8026ecb6>]
filemap_fault+0x1fa/0x3c6
Dec 17 15:54:33 turing-police kernel: [14503.403241] [<ffffffff8026cb6b>]
unlock_page+0x2d/0x31
Dec 17 15:54:33 turing-police kernel: [14503.403254] [<ffffffff8027925c>]
__do_fault+0x38d/0x3c3
Dec 17 15:54:33 turing-police kernel: [14503.403274] [<ffffffff8027ab68>]
handle_mm_fault+0x36d/0x6e9
Dec 17 15:54:33 turing-police kernel: [14503.403293] [<ffffffff80271903>]
__alloc_pages+0x68/0x2f6
Dec 17 15:54:33 turing-police kernel: [14503.403314] [<ffffffff802a510e>]
sys_mount+0x89/0xcb
Dec 17 15:54:33 turing-police kernel: [14503.403328] [<ffffffff80214f34>]
syscall_trace_enter+0x97/0x9b
Dec 17 15:54:33 turing-police kernel: [14503.403344] [<ffffffff8020c34c>]
tracesys+0xdc/0xe1
Dec 17 15:54:33 turing-police kernel: [14503.403359]
Dec 17 15:54:33 turing-police kernel: [14503.403366]
Dec 17 15:54:33 turing-police kernel: [14503.403367] Code: 48 8b 87 10 01 00 00
48 83 bf 38 02 00 00 40 48 8b 40 38 75
I don't mind it failing the mount, but the oops seems excessive. I suspect
that *somewhere* in that stack trace, we're wanting something like a
if (!foo_ptr)
return -EIO;
but I admit not being competent enough to decide where that should be.
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