[Bug 220491] usb_storage connected SD card disconnects/reconnects on resume from suspend

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=220491

--- Comment #48 from Paul Ausbeck (paula@alumni.cse.ucsc.edu) ---
I spent some time over the weekend instrumenting the kernel so that I could use
kdb to poke around kernel memory. I particularly wanted to examine the contents
of the variable reset_resume_delay which turned out to have the value of 0x1f4
as I was expecting. I first looked at /dev/mem as a method of reading kernel
memory but found that that method has been essentially deprecated and not
documented as so. I then instrumented for kdb/kgdb and eventually found that as
far as sysrq is concerned, the ativ9 left alt key is different from its right
alt key.

I then found that if kdb is active for long enough, kernel stalled, then once
the kernel again runs, the SD card reader will disconnect and reconnect
similarly to what happens sporadically on resume from suspend. I'm still not
certain about this observation. It hasn't happened enough times to be certain
of stall time requirements or even of correlation. I've just finished disabling
various systemd daemon watchdog timers that were confusing the issue. If this
kdb correlation turns out to be real, I think it should be a useful clue.

I've got a kdb breakpoint set on the usb_disconnect function. If I can figure
out how to keep the system from switching virtual consoles when it hits the
breakpoint, I will acquire a stack backtrace.

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