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There're few sysfs attributes in block layer which don't really need acquiring q->sysfs_lock while accessing it. The reason being, reading/ writing a value from/to such attributes are either atomic or could be easily protected using READ_ONCE()/WRITE_ONCE(). Moreover, sysfs attributes are inherently protected with sysfs/kernfs internal locking. So this change help segregate all existing sysfs attributes for which we could avoid acquiring q->sysfs_lock. For all read-only attributes we removed the q->sysfs_lock from show method of such attributes. In case attribute is read/write then we removed the q->sysfs_lock from both show and store methods of these attributes. We audited all block sysfs attributes and found following list of attributes which shouldn't require q->sysfs_lock protection: 1. io_poll: Write to this attribute is ignored. So, we don't need q->sysfs_lock. 2. io_poll_delay: Write to this attribute is NOP, so we don't need q->sysfs_lock. 3. io_timeout: Write to this attribute updates q->rq_timeout and read of this attribute returns the value stored in q->rq_timeout Moreover, the q->rq_timeout is set only once when we init the queue (under blk_mq_ init_allocated_queue()) even before disk is added. So that means that we don't need to protect it with q->sysfs_lock. As this attribute is not directly correlated with anything else simply using READ_ONCE/WRITE_ONCE should be enough. 4. nomerges: Write to this attribute file updates two q->flags : QUEUE_FLAG_ NOMERGES and QUEUE_FLAG_NOXMERGES. These flags are accessed during bio-merge which anyways doesn't run with q->sysfs_lock held. Moreover, the q->flags are updated/accessed with bitops which are atomic. So, protecting it with q->sysfs_lock is not necessary. 5. rq_affinity: Write to this attribute file makes atomic updates to q->flags: QUEUE_FLAG_SAME_COMP and QUEUE_FLAG_SAME_FORCE. These flags are also accessed from blk_mq_complete_need_ipi() using test_bit macro. As read/write to q->flags uses bitops which are atomic, protecting it with q->stsys_lock is not necessary. 6. nr_zones: Write to this attribute happens in the driver probe method (except nvme) before disk is added and outside of q->sysfs_lock or any other lock. Moreover nr_zones is defined as "unsigned int" and so reading this attribute, even when it's simultaneously being updated on other cpu, should not return torn value on any architecture supported by linux. So we can avoid using q->sysfs_lock or any other lock/ protection while reading this attribute. 7. discard_zeroes_data: Reading of this attribute always returns 0, so we don't require holding q->sysfs_lock. 8. write_same_max_bytes Reading of this attribute always returns 0, so we don't require holding q->sysfs_lock. Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Nilay Shroff <nilay@linux.ibm.com> Link: https://lore.kernel.org/r/20250304102551.2533767-4-nilay@linux.ibm.com Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.