From: Al Viro <viro@zeniv.linux.org.uk>
To: Shreeya Patel <shreeya.patel@collabora.com>
Cc: tytso@mit.edu, adilger.kernel@dilger.ca, krisman@collabora.com,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel@collabora.com
Subject: Re: [PATCH 1/2] fs: dcache: Handle case-exact lookup in d_alloc_parallel
Date: Sun, 3 Oct 2021 13:38:40 +0000 [thread overview]
Message-ID: <YVmyYP25kgGq9uEy@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <0b8fd2677b797663bfcb97f6aa108193fedf9767.1632909358.git.shreeya.patel@collabora.com>
On Wed, Sep 29, 2021 at 04:23:38PM +0530, Shreeya Patel wrote:
> There is a soft hang caused by a deadlock in d_alloc_parallel which
> waits up on lookups to finish for the dentries in the parent directory's
> hash_table.
> In case when d_add_ci is called from the fs layer's lookup functions,
> the dentry being looked up is already in the hash table (created before
> the fs lookup function gets called). We should not be processing the
> same dentry that is being looked up, hence, in case of case-insensitive
> filesystems we are making it a case-exact match to prevent this from
> happening.
NAK. What you are doing would lead to parallel calls of ->lookup() in the
same directory for names that would compare as equal. Which violates
all kinds of assumptions in the analysis of dentry tree locking.
d_add_ci() is used to force the "exact" spelling of the name on lookup -
that's the whole point of that thing. What are you trying to achieve,
and what's the point of mixing that with non-trivial ->d_compare()?
If it's "force to exact spelling on lookup, avoid calling ->lookup() on
aliases", d_add_ci() is simply not a good match.
next prev parent reply other threads:[~2021-10-03 13:43 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 10:53 [PATCH 0/2] Handle a soft hang and the inconsistent name issue Shreeya Patel
2021-09-29 10:53 ` [PATCH 1/2] fs: dcache: Handle case-exact lookup in d_alloc_parallel Shreeya Patel
2021-10-01 18:35 ` Gabriel Krisman Bertazi
2021-10-03 13:52 ` Al Viro
2021-10-03 13:38 ` Al Viro [this message]
2021-10-05 13:09 ` Shreeya Patel
2021-09-29 10:53 ` [PATCH 2/2] fs: ext4: Fix the inconsistent name exposed by /proc/self/cwd Shreeya Patel
2021-10-01 18:41 ` Theodore Ts'o
2021-10-01 19:11 ` Gabriel Krisman Bertazi
2021-10-02 1:21 ` Theodore Ts'o
2021-10-14 21:54 ` Gabriel Krisman Bertazi
2021-10-01 18:16 ` [PATCH 0/2] Handle a soft hang and the inconsistent name issue Gabriel Krisman Bertazi
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