Re: [PATCH, RESEND] Avoid that SCSI device removal through sysfs triggers a deadlock

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On Thu, 2018-07-26 at 06:35 -0700, Tejun Heo wrote:
+AD4- Making removal asynchronous this way sometimes causes issues because
+AD4- whether the user sees the device released or not is racy.
+AD4- kernfs/sysfs have mechanisms to deal with these cases - remove+AF8-self
+AD4- and kernfs+AF8-break+AF8-active+AF8-protection().  Have you looked at those?

Hello Tejun,

The call stack in the patch description shows that sdev+AF8-store+AF8-delete() is
involved in the deadlock. The implementation of that function is as follows:

static ssize+AF8-t
sdev+AF8-store+AF8-delete(struct device +ACo-dev, struct device+AF8-attribute +ACo-attr,
		  const char +ACo-buf, size+AF8-t count)
+AHs-
	if (device+AF8-remove+AF8-file+AF8-self(dev, attr))
		scsi+AF8-remove+AF8-device(to+AF8-scsi+AF8-device(dev))+ADs-
	return count+ADs-
+AH0AOw-

device+AF8-remove+AF8-file+AF8-self() calls sysfs+AF8-remove+AF8-file+AF8-self() and that last
function calls kernfs+AF8-remove+AF8-self(). In other words, kernfs+AF8-remove+AF8-self()
is already being used. Please let me know if I misunderstood your comment.

Thanks,

Bart.




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