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SubjectRe: [PATCH v2] ubifs: Fix deadlock in concurrent bulk-read and writepage
On Sat, Jan 11, 2020 at 10:43 AM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
>
> In ubifs, concurrent execution of writepage and bulk read on the same file
> may cause ABBA deadlock, for example (Reproduce method see Link):
>
> Process A(Bulk-read starts from page4) Process B(write page4 back)
> vfs_read wb_workfn or fsync
> ... ...
> generic_file_buffered_read write_cache_pages
> ubifs_readpage LOCK(page4)
>
> ubifs_bulk_read ubifs_writepage
> LOCK(ui->ui_mutex) ubifs_write_inode
>
> ubifs_do_bulk_read LOCK(ui->ui_mutex)
> find_or_create_page(alloc page4) ↑
> LOCK(page4) <-- ABBA deadlock occurs!
>
> In order to ensure the serialization execution of bulk read, we can't
> remove the big lock 'ui->ui_mutex' in ubifs_bulk_read(). Instead, we
> allow ubifs_do_bulk_read() to lock page failed by replacing
> find_or_create_page(FGP_LOCK) with
> pagecache_get_page(FGP_LOCK | FGP_NOWAIT).
>
> Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
> Suggested-by: zhangyi (F) <yi.zhang@huawei.com>
> Cc: <Stable@vger.kernel.org>
> Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
> ---
> fs/ubifs/file.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)

Applied. Thanks a lot for hunting this down!

--
Thanks,
//richard

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