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SubjectRe: [PATCH] mm: save current->journal_info before calling fault/page_mkwrite
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Am 13.12.2017 um 04:58 schrieb Yan, Zheng:
> We recently got an Oops report:
>
> BUG: unable to handle kernel NULL pointer dereference at (null)
> IP: jbd2__journal_start+0x38/0x1a2
> [...]
> Call Trace:
> ext4_page_mkwrite+0x307/0x52b
> _ext4_get_block+0xd8/0xd8
> do_page_mkwrite+0x6e/0xd8
> handle_mm_fault+0x686/0xf9b
> mntput_no_expire+0x1f/0x21e
> __do_page_fault+0x21d/0x465
> dput+0x4a/0x2f7
> page_fault+0x22/0x30
> copy_user_generic_string+0x2c/0x40
> copy_page_to_iter+0x8c/0x2b8
> generic_file_read_iter+0x26e/0x845
> timerqueue_del+0x31/0x90
> ceph_read_iter+0x697/0xa33 [ceph]
> hrtimer_cancel+0x23/0x41
> futex_wait+0x1c8/0x24d
> get_futex_key+0x32c/0x39a
> __vfs_read+0xe0/0x130
> vfs_read.part.1+0x6c/0x123
> handle_mm_fault+0x831/0xf9b
> __fget+0x7e/0xbf
> SyS_read+0x4d/0xb5
>
> The reason is that page fault can happen when one filesystem copies
> data from/to userspace, the filesystem may set current->journal_info.
> If the userspace memory is mapped to a file on another filesystem,
> the later filesystem may also want to use current->journal_info.
>
> Signed-off-by: "Yan, Zheng" <zyan@redhat.com>

Reported-and-tested-by: Amon Ott <a.ott@m-privacy.de>

Thanks a lot for the patch! I have ported your patch to 4.9.68, tested
and the bug seems fixed now.

Amon Ott
--
Dr. Amon Ott
m-privacy GmbH Tel: +49 30 24342334
Werner-Voß-Damm 62 Fax: +49 30 99296856
12101 Berlin http://www.m-privacy.de

Amtsgericht Charlottenburg, HRB 84946

Geschäftsführer:
Dipl.-Kfm. Holger Maczkowsky,
Roman Maczkowsky

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