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For attributes that control queue limits, the > store operation will also lock the queue limits with a call to > queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may > need to issue commands to a device to obtain limit values from the > hardware with the queue limits locked. This creates a potential ABBA > deadlock situation if a user attempts to modify a limit (thus freezing > the device queue) while the device driver starts a revalidation of the > device queue limits. > > Avoid such deadlock by not freezing the queue before calling the > ->store_limit() method in struct queue_sysfs_entry and instead use the > queue_limits_commit_update_frozen helper to freeze the queue after taking > the limits lock. > > This also removes taking the sysfs lock for the store_limit method as > it doesn't protect anything here, but creates even more nesting. > Hopefully it will go away from the actual sysfs methods entirely soon. Do you mean that the sysfs_lock could be removed in future? I would have thought that queue limits lock could be used for the same thing, but I am probably failing to see some lock nesting/ordering issues...