On 01/04/2015 11:59 AM, hujianyang wrote: > I think this exporting of .remount_fs may allow people in userspace have the ability to remount a filesystem with a new set of mounting options. Your new adding function do nothing with the passing in parameters. I'm not sure if it could be competent for remount case. Add Cc linux-unionfs. Hi hujianyang, I think it makes no difference whether .remount_fs is exported or not, except in the read-write mount case. And the patch's use case is below: Before patch: root@qemux86:~# mount -t overlay overlay -olowerdir=lower:lower2 merged mount: warning: merged seems to be mounted read-only. root@qemux86:~# mount | grep overlay overlay on /home/root/merged type overlay (ro,relatime,lowerdir=lower:lower2) root@qemux86:~# mount -o remount,rw merged root@qemux86:~# mount | grep overlay overlay on /home/root/merged type overlay (rw,relatime,lowerdir=lower:lower2) root@qemux86:~# echo hi > merged/hi [ 95.906739] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [ 95.907172] IP: [<ffffffff8117e0b6>] mnt_want_write+0x16/0x50 [ 95.907172] PGD 1e34e067 PUD 1e20a067 PMD 0 [ 95.907172] Oops: 0000 [#1] SMP [ 95.907172] Modules linked in: [ 95.907172] CPU: 0 PID: 1358 Comm: sh Not tainted 3.19.0-rc2-next-20141231+ #5 [ 95.907172] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 [ 95.907172] task: ffff88001dad2d00 ti: ffff88001d4dc000 task.ti: ffff88001d4dc000 [ 95.907172] RIP: 0010:[<ffffffff8117e0b6>] [<ffffffff8117e0b6>] mnt_want_write+0x16/0x50 [ 95.907172] RSP: 0000:ffff88001d4dfbf8 EFLAGS: 00000292 [ 95.907172] RAX: ffff88001da4ac80 RBX: 0000000000000000 RCX: 0000000000000000 [ 95.907172] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000000 [ 95.907172] RBP: ffff88001d4dfc18 R08: 0000000000000000 R09: 0000000000000000 [ 95.907172] R10: 0000000000000000 R11: ffff88000080fb40 R12: 00000000000081a4 [ 95.907172] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 [ 95.907172] FS: 0000000000000000(0003) GS:ffff88001fc00000(0063) knlGS:00000000f7755b40 [ 95.907172] CS: 0010 DS: 002b ES: 002b CR0: 000000008005003b [ 95.907172] CR2: 0000000000000008 CR3: 000000001d4bc000 CR4: 00000000000006f0 [ 95.907172] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 95.907172] DR3: 0000000000000000 DR6: 0000000000000000 DR7: 0000000000000000 [ 95.907172] Stack: [ 95.907172] 0000000000000000 00000003000081a4 ffffffff0000000a ffff88000080fb40 [ 95.907172] ffff88001d4dfc28 ffffffff8128ca97 ffff88001d4dfc68 ffffffff8128f1e0 [ 95.907172] ffff88001dd55c70 ffff88000080fb40 0000000000000000 ffff88001dd55c70 [ 95.907172] Call Trace: [ 95.907172] [<ffffffff8128ca97>] ovl_want_write+0x17/0x20 [ 95.907172] [<ffffffff8128f1e0>] ovl_create_object+0x20/0x60 [ 95.907172] [<ffffffff8128f2be>] ovl_create+0x1e/0x20 [ 95.907172] [<ffffffff8116aabd>] vfs_create+0xcd/0x130 [ 95.907172] [<ffffffff8116d572>] do_last+0x962/0x1110 [ 95.907172] [<ffffffff8116b97c>] ? path_init+0xbc/0x450 [ 95.907172] [<ffffffff8116dd9f>] path_openat+0x7f/0x620 [ 95.907172] [<ffffffff81136aa0>] ? handle_mm_fault+0x5e0/0xa30 [ 95.907172] [<ffffffff8116fd05>] do_filp_open+0x35/0x90 [ 95.907172] [<ffffffff8116ecda>] ? getname_flags+0x4a/0x1a0 [ 95.907172] [<ffffffff8117bcdd>] ? __alloc_fd+0x7d/0x120 [ 95.907172] [<ffffffff8115ea23>] do_sys_open+0x123/0x220 [ 95.907172] [<ffffffff811aadc6>] compat_SyS_open+0x16/0x20 [ 95.907172] [<ffffffff8184ea89>] ia32_do_call+0x13/0x13 [ 95.907172] Code: c3 0f 1f 40 00 48 8b 47 28 65 ff 48 04 b8 e2 ff ff ff 5d c3 90 55 ba 01 00 00 00 be 01 00 00 00 48 89 e5 53 48 89 fb 48 83 ec 18 <48> 8b 7f 08 e8 31 3c fe ff 48 89 df e8 79 ff ff ff 85 c0 74 14 [ 95.907172] RIP [<ffffffff8117e0b6>] mnt_want_write+0x16/0x50 [ 95.907172] RSP <ffff88001d4dfbf8> [ 95.907172] CR2: 0000000000000008 [ 95.919596] ---[ end trace 770a329b637fe67d ]--- After patch: root@qemux86:~# mount -t overlay overlay -olowerdir=lower:lower2 merged mount: warning: merged seems to be mounted read-only. root@qemux86:~# mount | grep overlay overlay on /home/root/merged type overlay (ro,relatime,lowerdir=lower:lower2) root@qemux86:~# mount -o remount,rw merged mount: warning: /home/root/merged seems to be mounted read-only. root@qemux86:~# mount | grep overlay overlay on /home/root/merged type overlay (ro,relatime,lowerdir=lower:lower2) root@qemux86:~# echo hi > merged/hi -sh: merged/hi: Read-only file system root@qemux86:~# If what I think is incorrect, please let me know. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
