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Jean-Sébastien Pédron
3a55e76b84
Initially, `zfs_getpages()` is provided with an array of busy pages by
the vnode pager. It then tries to acquire the range lock, but if there
is a concurrent `zfs_write()` running and fails to acquire that range
lock, it "unbusies" the pages to avoid a deadlock with `zfs_write()`.
After that, it grabs the pages again and retries to acquire the range
lock, and so on.
Once it got the range lock, it filters out valid pages, then copy DMU
data to the remaining invalid pages.
The problem is that freshly allocated zero'd pages it grabbed itself are
marked as valid. Therefore they are skipped by the second part of the
function and DMU data is never copied to these pages. This causes mapped
pages to contain zeros instead of the expected file content.
This was discovered while working on RabbitMQ on FreeBSD. I could
reproduce the problem easily with the following commands:
git clone https://github.com/rabbitmq/rabbitmq-server.git
cd rabbitmq-server/deps/rabbit
gmake distclean-ct RABBITMQ_METADATA_STORE=mnesia \
ct-amqp_client t=cluster_size_3:leader_transfer_stream_send
The testsuite fails because there is a sendfile(2) that can happen
concurrently to a write(2) on the same file. This leads to sendfile(2)
or read(2) (after the sendfile) sending/returning data with zeros, which
causes a function to crash.
The patch consists of not setting the `VM_ALLOC_ZERO` flag when
`zfs_getpages()` grabs pages again. Then, the last page is zero'd if it
is invalid, in case it would be partially filled with the end of the
file content. Other pages are either valid (and will be skipped) or they
will be entirely overwritten by the file content.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Mark Johnston <markj@FreeBSD.org>
Signed-off-by: Jean-Sébastien Pédron <dumbbell@FreeBSD.org>
Closes #17851
OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 13.0-RELEASE.