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From: Al Viro <viro@zeniv.linux.org.uk>
To: "zhengbin (A)" <zhengbin13@huawei.com>
Cc: jack@suse.cz, akpm@linux-foundation.org,
	linux-fsdevel@vger.kernel.org,
	"zhangyi (F)" <yi.zhang@huawei.com>,
	renxudong1@huawei.com, Hou Tao <houtao1@huawei.com>
Subject: Re: Possible FS race condition between iterate_dir and d_alloc_parallel
Date: Mon, 9 Sep 2019 15:59:10 +0100	[thread overview]
Message-ID: <20190909145910.GG1131@ZenIV.linux.org.uk> (raw)
In-Reply-To: <afdfa1f4-c954-486b-1eb2-efea6fcc2e65@huawei.com>

On Mon, Sep 09, 2019 at 10:10:00PM +0800, zhengbin (A) wrote:

Hmm...  So your theory is that what you are seeing is the insertion
into the list done by list_add() exposing an earlier ->next pointer
to those who might be doing lockless walk through the list.
Potentially up to the last barrier done before the list_add()...

> We can solute it in 2 ways:
> 
> 1. add a smp_wmb between __d_alloc and list_add(&dentry->d_child, &parent->d_subdirs)
> 2. revert commit ebaaa80e8f20 ("lockless next_positive()")

I want to take another look at the ->d_subdirs/->d_child readers...
I agree that the above sounds plausible, but I really want to be
sure about the exclusion we have for those accesses.

I'm not sure that smp_wmb() alone would suffice, BTW - the reader side
loop would need to be careful as well.

Which architecture it was, again?  arm64?

  reply	other threads:[~2019-09-09 14:59 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-03 14:44 Possible FS race condition between iterate_dir and d_alloc_parallel zhengbin (A)
2019-09-03 15:40 ` Al Viro
2019-09-03 15:41   ` Al Viro
2019-09-04  6:15     ` zhengbin (A)
2019-09-05 17:47       ` Al Viro
2019-09-06  0:55         ` Jun Li
2019-09-06  2:00           ` Al Viro
2019-09-06  2:32         ` zhengbin (A)
2019-09-09 14:10       ` zhengbin (A)
2019-09-09 14:59         ` Al Viro [this message]
2019-09-09 15:10           ` zhengbin (A)
     [not found]             ` <7e32cda5-dc89-719d-9651-cf2bd06ae728@huawei.com>
2019-09-10 21:53               ` Al Viro
2019-09-10 22:17                 ` Al Viro
2019-09-14 16:16                 ` [PATCH] " Al Viro
2019-09-14 16:49                   ` Linus Torvalds
2019-09-14 17:01                     ` Al Viro
2019-09-14 17:15                       ` Linus Torvalds
2019-09-14 20:04                         ` Al Viro
2019-09-14 22:57                           ` Linus Torvalds
2019-09-15  0:50                             ` Al Viro
2019-09-15  1:41                               ` Linus Torvalds
2019-09-15 16:02                                 ` Al Viro
2019-09-15 17:58                                   ` Linus Torvalds
2019-09-21 14:07                                     ` Al Viro
2019-09-21 16:21                                       ` Linus Torvalds
2019-09-21 17:18                                         ` Al Viro
2019-09-21 17:38                                           ` Linus Torvalds
2019-09-24  2:52                                       ` Al Viro
2019-09-24 13:30                                         ` Josef Bacik
2019-09-24 14:51                                           ` Al Viro
2019-09-24 15:01                                             ` Josef Bacik
2019-09-24 15:11                                               ` Al Viro
2019-09-24 15:26                                                 ` Josef Bacik
2019-09-24 16:33                                                   ` Al Viro
     [not found]                                         ` <CAHk-=wiJ1eY7y6r_cFNRPCqD+BJZS7eJeQFO6OrXxRFjDAipsQ@mail.gmail.com>
2019-09-29  5:29                                           ` Al Viro
2019-09-25 11:59                                       ` Amir Goldstein
2019-09-25 12:22                                         ` Al Viro
2019-09-25 12:34                                           ` Amir Goldstein
2019-09-22 21:29                     ` Al Viro
2019-09-23  3:32                       ` zhengbin (A)
2019-09-23  5:08                         ` Al Viro
     [not found]                   ` <20190916020434.tutzwipgs4f6o3di@inn2.lkp.intel.com>
2019-09-16  2:58                     ` 266a9a8b41: WARNING:possible_recursive_locking_detected Al Viro
2019-09-16  3:03                       ` Al Viro
2019-09-16  3:44                         ` Linus Torvalds
2019-09-16 17:16                           ` Al Viro
2019-09-16 17:29                             ` Al Viro
     [not found]                             ` <bd707e64-9650-e9ed-a820-e2cabd02eaf8@huawei.com>
2019-09-17 12:01                               ` Al Viro
2019-09-19  3:36                                 ` zhengbin (A)
2019-09-19  3:55                                   ` Al Viro

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