Re: 2.6.23-rc1-mm1

From: Andrew Morton
Date: Mon Jul 30 2007 - 14:33:27 EST

On Mon, 30 Jul 2007 09:58:34 +0000
"Dave Young" <hidave.darkstar@xxxxxxxxx> wrote:

> > Hi,
> > I get an oops when trying to mount an ISO file using the loopback device.
> > If I revert the patch 'loop-use-unlocked_ioctl.patch' the mount works.
> >
> > Here's the oops:
> >
> > [ 85.697033] Unable to handle kernel NULL pointer dereference at 0000000000000100 RIP:
> > [ 85.702528] [<ffffffff80477885>] lo_ioctl+0x25/0xaa0
> > [ 85.710066] PGD 73fd067 PUD 735b067 PMD 0
> > [ 85.714221] Oops: 0000 [1] PREEMPT SMP
> > [ 85.718117] CPU 1
> > [ 85.720159] Modules linked in:
> > [ 85.723242] Pid: 3976, comm: mount Not tainted 2.6.23-rc1-mm1 #4
> > [ 85.729247] RIP: 0010:[<ffffffff80477885>] [<ffffffff80477885>] lo_ioctl+0x25/0xaa0
> > [ 85.737011] RSP: 0018:ffff8100076a3708 EFLAGS: 00010282
> > [ 85.742326] RAX: ffffffff80477860 RBX: 00000000fffffdfd RCX: 0000000000005310
> > [ 85.749459] RDX: ffff8100076a3b58 RSI: 0000000000005310 RDI: 0000000000000000
> > [ 85.756591] RBP: ffff8100076a3908 R08: ffff8100076a3b58 R09: ffff81000649da80
> > [ 85.763723] R10: 0000000000000000 R11: 2222222222222222 R12: 0000000000005310
> > [ 85.770856] R13: ffff8100076a3b58 R14: 0000000000005310 R15: 0000000000000000
> > [ 85.777988] FS: 00002b4fab3a0e20(0000) GS:ffff810004017180(0000) knlGS:0000000000000000
> > [ 85.786081] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [ 85.791829] CR2: 0000000000000100 CR3: 00000000073d7000 CR4: 00000000000006e0
> > [ 85.798970] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [ 85.806102] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > [ 85.813235] Process mount (pid: 3976, threadinfo ffff8100076a2000, task ffff8100062f66d0)
> > [ 85.821413] Stack: 0000000200000001 ffff8100062f6e90 ffff8100062f6e90 000000000013638a
> > [ 85.829533] ffffffff80a78ef0 0000000000000000 ffff8100076a37b8 ffffffff8025c690
> > [ 85.837020] ffff8100062f66d0 ffff8100062f6e58 0000000200000001 0000000000000000
> > [ 85.844308] Call Trace:
> > [ 85.846961] [<ffffffff8025c690>] __lock_acquire+0x3d0/0x1170
> > [ 85.852715] [<ffffffff8025baee>] mark_held_locks+0x3e/0x80
> > [ 85.858290] [<ffffffff8064ff0a>] __mutex_lock_slowpath+0x1ca/0x330
> > [ 85.864565] [<ffffffff8025baee>] mark_held_locks+0x3e/0x80
> > [ 85.870139] [<ffffffff8064fd39>] mutex_unlock+0x9/0x10
> > [ 85.875366] [<ffffffff8064fc69>] __mutex_unlock_slowpath+0xd9/0x1a0
> > [ 85.881720] [<ffffffff8025bcca>] trace_hardirqs_on+0xda/0x180
> > [ 85.887555] [<ffffffff8064fd39>] mutex_unlock+0x9/0x10
> > [ 85.892782] [<ffffffff802c3ba1>] do_open+0x231/0x320
> > [ 85.897839] [<ffffffff803b7113>] blkdev_driver_ioctl+0x43/0x90
> > [ 85.903758] [<ffffffff803b7429>] blkdev_ioctl+0x2c9/0x780
> > [ 85.909247] [<ffffffff8065149d>] trace_hardirqs_on_thunk+0x35/0x37
> > [ 85.915522] [<ffffffff8020c320>] restore_args+0x0/0x30
> > [ 85.920751] [<ffffffff802c2d60>] kill_bdev+0x0/0x40
> > [ 85.925718] [<ffffffff802c4084>] ioctl_by_bdev+0x34/0x50
> > [ 85.931119] [<ffffffff80336019>] isofs_fill_super+0x969/0xaf0
> > [ 85.936954] [<ffffffff80299b9c>] sget+0x3c/0x3f0
> > [ 85.941662] [<ffffffff80299760>] test_bdev_super+0x0/0x20
> > [ 85.947150] [<ffffffff80651fc0>] _spin_unlock+0x30/0x60
> > [ 85.952464] [<ffffffff80299760>] test_bdev_super+0x0/0x20
> > [ 85.957951] [<ffffffff80299f4a>] sget+0x3ea/0x3f0
> > [ 85.962747] [<ffffffff803c662f>] strlcpy+0x4f/0x70
> > [ 85.967628] [<ffffffff8029aa9c>] get_sb_bdev+0x15c/0x190
> > [ 85.973029] [<ffffffff803356b0>] isofs_fill_super+0x0/0xaf0
> > [ 85.978693] [<ffffffff80334fb3>] isofs_get_sb+0x13/0x20
> > [ 85.984006] [<ffffffff8029a4c8>] vfs_kern_mount+0x58/0xc0
> > [ 85.989494] [<ffffffff802b2366>] do_mount+0x206/0x850
> > [ 85.994635] [<ffffffff8027b891>] __mod_zone_page_state+0x21/0x90
> > [ 86.000729] [<ffffffff80273160>] rmqueue_bulk+0x90/0xb0
> > [ 86.006043] [<ffffffff80651fc0>] _spin_unlock+0x30/0x60
> > [ 86.011358] [<ffffffff80273160>] rmqueue_bulk+0x90/0xb0
> > [ 86.016673] [<ffffffff80274425>] get_page_from_freelist+0x395/0x500
> > [ 86.023026] [<ffffffff8025bcca>] trace_hardirqs_on+0xda/0x180
> > [ 86.028860] [<ffffffff802742b3>] get_page_from_freelist+0x223/0x500
> > [ 86.035213] [<ffffffff80274639>] __alloc_pages+0x59/0x3a0
> > [ 86.040702] [<ffffffff80246d68>] sigprocmask+0x38/0xf0
> > [ 86.045929] [<ffffffff802940e8>] kmem_cache_alloc+0x98/0xd0
> > [ 86.051590] [<ffffffff80274a00>] __get_free_pages+0x80/0x90
> > [ 86.057251] [<ffffffff802b2a44>] sys_mount+0x94/0xf0
> > [ 86.062305] [<ffffffff8065149d>] trace_hardirqs_on_thunk+0x35/0x37
> > [ 86.068572] [<ffffffff8020bd7e>] system_call+0x7e/0x83
> > [ 86.073799]
> > [ 86.075296] INFO: lockdep is turned off.
> > [ 86.079226]
> > [ 86.079227] Code: 48 8b 87 00 01 00 00 49 89 d6 48 8b 18 48 8b 83 10 03 00 00
> > [ 86.088306] RIP [<ffffffff80477885>] lo_ioctl+0x25/0xaa0
> > [ 86.093734] RSP <ffff8100076a3708>
> > [ 86.097231] CR2: 0000000000000100
> >
>
> Hi, andrew,
> I debugged this problem. The oops is caused by NUll file pointer.
>
> I change the unlocked_ioctl to ioctl in fops. print some debug info :
> [ 51.018272] hidave ### cmd : get_status
> [ 51.018281] hidave ### cmd : 19459 inode : c2024b9c file : c2e89c00
> [ 51.052419] hidave ### cmd : set_fd
> [ 51.052426] hidave ### cmd : 19456 inode : c2024b9c file : c2e89100
> [ 51.052494] hidave ### cmd : set_status64
> [ 51.052500] hidave ### cmd : 19460 inode : c2024b9c file : c2e89100
> [ 51.125241] hidave ### cmd : unknown
> >>(The 21264 cmd is a cdrom ioctl command.)
> [ 51.125248] hidave ### cmd : 21264 inode : c2024b9c file : 00000000
> >>if use ioctl interface the inode is transfered, but in the
> unlocked_ioctl interface only the file pointer is transfered, so NULL
> caused the panic.
>
> PS: I noticed the fs/block_dev.c: line 1374:
> res = blkdev_ioctl(bdev->bd_inode, NULL, cmd, arg);
>
> So, just changeback from unlocked_ioctl to ioctl, the lock_kernel
> remove is still ok.

ho hum, crap. Yes, ioctl_by_bdev() doesn't have a file* and so it makes
unlocked_ioctl() rather tricky. We could cook up a `struct file' on the
stack (we do that in various places), but that sucks.

Christoph, have you any clever suggestions?

Thanks.


From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

The last lock_kernel() has disappeared from loop.c. Switch it over to using
unlocked_ioctl.

Cc: Diego Woitasen <diego@xxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

drivers/block/loop.c | 12 +++++++-----
1 files changed, 7 insertions(+), 5 deletions(-)

diff -puN drivers/block/loop.c~loop-use-unlocked_ioctl drivers/block/loop.c
--- a/drivers/block/loop.c~loop-use-unlocked_ioctl
+++ a/drivers/block/loop.c
@@ -1124,12 +1124,14 @@ loop_get_status64(struct loop_device *lo
return err;
}

-static int lo_ioctl(struct inode * inode, struct file * file,
- unsigned int cmd, unsigned long arg)
+static long lo_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
- struct loop_device *lo = inode->i_bdev->bd_disk->private_data;
+ struct inode *inode;
+ struct loop_device *lo;
int err;

+ inode = file->f_mapping->host;
+ lo = inode->i_bdev->bd_disk->private_data;
mutex_lock(&lo->lo_ctl_mutex);
switch (cmd) {
case LOOP_SET_FD:
@@ -1304,7 +1306,7 @@ static long lo_compat_ioctl(struct file
arg = (unsigned long) compat_ptr(arg);
case LOOP_SET_FD:
case LOOP_CHANGE_FD:
- err = lo_ioctl(inode, file, cmd, arg);
+ err = lo_ioctl(file, cmd, arg);
break;
default:
err = -ENOIOCTLCMD;
@@ -1340,7 +1342,7 @@ static struct block_device_operations lo
.owner = THIS_MODULE,
.open = lo_open,
.release = lo_release,
- .ioctl = lo_ioctl,
+ .unlocked_ioctl = lo_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = lo_compat_ioctl,
#endif
_

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