On Thu, Feb 06, 2020 at 08:20:48PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f5de5b83303e61b1f3fb09bd77ce3ac2d7a475f2 Mon Sep 17 00:00:00 2001
From: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Date: Sat, 11 Jan 2020 17:50:36 +0800
Subject: [PATCH] ubifs: Fix deadlock in concurrent bulk-read and writepage
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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@xxxxxxxxxx>
Suggested-by: zhangyi (F) <yi.zhang@xxxxxxxxxx>
Cc: <Stable@xxxxxxxxxxxxxxx>
Fixes: 4793e7c5e1c ("UBIFS: add bulk-read facility")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206153
Signed-off-by: Richard Weinberger <richard@xxxxxx>
I took in 480a1a6a3ef6 ("ubifs: Change gfp flags in page allocation for
bulk read") as dependency and queued both for 4.9 and 4.4.
--
Thanks,
Sasha
