I was trying to get rid of the in in_softirq() in ezusb_req_ctx_wait()
within the orinoco usb driver,
drivers/net/wireless/intersil/orinoco/orinoco_usb.c. A small snippet:
| static void ezusb_req_ctx_wait(struct ezusb_priv *upriv,
| struct request_context *ctx)
…
| if (in_softirq()) {
| /* If we get called from a timer, timeout timers don't
| * get the chance to run themselves. So we make sure
| * that we don't sleep for ever */
| int msecs = DEF_TIMEOUT * (1000 / HZ);
|
| while (!try_wait_for_completion(&ctx->done) && msecs--)
| udelay(1000);
| } else {
| wait_for_completion(&ctx->done);
…
| }
This is broken. The EHCI and XHCI HCD will complete the URB in
BH/tasklet. Should we ever get here in_softirq() then we will spin
here/wait here until the timeout passes because the tasklet won't be
able to run. OHCI/UHCI HCDs still complete in hard-IRQ so it would work
here.
Is it possible to end up here in softirq context or is this a relic?
Well I have no hardware but I see this:
orinoco_set_monitor_channel() [I assume that this is fully preemtible]
-> orinoco_lock() [this should point to ezusb_lock_irqsave() which
does spin_lock_bh(lock), so from here on
in_softirq() returns true]
-> hw->ops->cmd_wait() [-> ezusb_docmd_wait()]
-> ezusb_alloc_ctx() [ sets ctx->in_rid to EZUSB_RID_ACK/0x0710 ]
-> ezusb_access_ltv()
-> if (ctx->in_rid)
-> ezusb_req_ctx_wait(upriv, ctx);
-> ctx->state should be EZUSB_CTX_REQ_COMPLETE so we end up in
the while loop above. So we udelay() 3 * 1000 * 1ms = 3sec.
-> Then ezusb_access_ltv() should return with an error due to
timeout.
This isn't limited to exotic features like monitor mode. orinoco_open()
does orinoco_lock() followed by orinoco_hw_program_rids() which in the
end invokes ezusb_write_ltv(,, EZUSB_RID_ACK) which is non-zero and also
would block (ezusb_xmit() would use 0 as the last argument so it won't
block).
I don't see how this driver can work on EHCI/XHCI HCD as of today.
The driver is an orphan since commit
3a59babbee409 ("orinoco: update status in MAINTAINERS")
which is ten years ago. If I replace in_softirq() with a `may_sleep'
argument then it is still broken.
Should it be removed?
Sebastian
