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Shin'ichiro Kawasaki ffed586b8c scsi: sd: Move sd_read_cpr() out of the q->limits_lock region 
Commit 804e498e04 ("sd: convert to the atomic queue limits API")
introduced pairs of function calls to queue_limits_start_update() and
queue_limits_commit_update(). These two functions lock and unlock
q->limits_lock. In sd_revalidate_disk(), sd_read_cpr() is called after
queue_limits_start_update() call and before queue_limits_commit_update()
call. sd_read_cpr() locks q->sysfs_dir_lock and &q->sysfs_lock. Then new
lock dependencies were created between q->limits_lock, q->sysfs_dir_lock
and q->sysfs_lock, as follows:

sd_revalidate_disk
  queue_limits_start_update
    mutex_lock(&q->limits_lock)
  sd_read_cpr
    disk_set_independent_access_ranges
      mutex_lock(&q->sysfs_dir_lock)
      mutex_lock(&q->sysfs_lock)
      mutex_unlock(&q->sysfs_lock)
      mutex_unlock(&q->sysfs_dir_lock)
  queue_limits_commit_update
    mutex_unlock(&q->limits_lock)

However, the three locks already had reversed dependencies in other
places. Then the new dependencies triggered the lockdep WARN "possible
circular locking dependency detected" [1]. This WARN was observed by
running the blktests test case srp/002.

To avoid the WARN, move the sd_read_cpr() call in sd_revalidate_disk()
after the queue_limits_commit_update() call. In other words, move the
sd_read_cpr() call out of the q->limits_lock region.

[1] https://lore.kernel.org/linux-scsi/vlmv53ni3ltwxplig5qnw4xsl2h6ccxijfbqzekx76vxoim5a5@dekv7q3es3tx/

Fixes: 804e498e04 ("sd: convert to the atomic queue limits API")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20240801054234.540532-1-shinichiro.kawasaki@wdc.com
Tested-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
History 2024-08-01 22:02:34 -04:00
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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.