linux-kernel - [GIT PULL] netfs: Potential deadlock and error handling fixes

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Message-ID: <2420479.1638912905@warthog.procyon.org.uk>
Date:   Tue, 07 Dec 2021 21:35:05 +0000
From:   David Howells <dhowells@...hat.com>
To:     torvalds@...ux-foundation.org
cc:     dhowells@...hat.com, Jeffle Xu <jefflexu@...ux.alibaba.com>,
        jlayton@...nel.org, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>, linux-cachefs@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [GIT PULL] netfs: Potential deadlock and error handling fixes

Hi Linus,

Could you pull these fixes for the netfs lib?  There are two:

 (1) Fix a lockdep warning and potential deadlock.  This is takes the
     simple approach of offloading the write-to-cache done from within a
     network filesystem read to a worker thread to avoid taking the
     sb_writer lock from the cache backing filesystem whilst holding the
     mmap lock on an inode from the network filesystem.

     Jan Kara posits a scenario whereby this can cause deadlock[1], though
     it's quite complex and I think requires someone in userspace to
     actually do I/O on the cache files.  Matthew Wilcox isn't so certain,
     though[2].

     An alternative way to fix this, suggested by Darrick Wong, might be to
     allow cachefiles to prevent userspace from performing I/O upon the
     file - something like an exclusive open - but that's beyond the scope
     of a fix here if we do want to make such a facility in the future.

 (2) In some of the error handling paths where netfs_ops->cleanup() is
     called, the arguments are transposed[3].  gcc doesn't complain because
     one of the parameters is void* and one of the values is void*.

David

Link: https://lore.kernel.org/r/20210922110420.GA21576@quack2.suse.cz/ [1]
Link: https://lore.kernel.org/r/Ya9eDiFCE2fO7K/S@casper.infradead.org/ [2]
Link: https://lore.kernel.org/r/20211207031449.100510-1-jefflexu@linux.alibaba.com/ [3]

---
The following changes since commit 0fcfb00b28c0b7884635dacf38e46d60bf3d4eb1:

  Linux 5.16-rc4 (2021-12-05 14:08:22 -0800)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git tags/netfs-fixes-20211207

for you to fetch changes up to 3cfef1b612e15a0c2f5b1c9d3f3f31ad72d56fcd:

  netfs: fix parameter of cleanup() (2021-12-07 15:47:09 +0000)

----------------------------------------------------------------
netfslib fixes

----------------------------------------------------------------
David Howells (1):
      netfs: Fix lockdep warning from taking sb_writers whilst holding mmap_lock

Jeffle Xu (1):
      netfs: fix parameter of cleanup()

 fs/netfs/read_helper.c | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)