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Endless loop in uart pipe #5298

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erwango opened this issue Dec 6, 2017 · 3 comments
Closed

Endless loop in uart pipe #5298

erwango opened this issue Dec 6, 2017 · 3 comments
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@erwango
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area: UART Universal Asynchronous Receiver-Transmitter platform: STM32 ST Micro STM32
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v1.10.0

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@erwango
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erwango commented Dec 6, 2017

Reported in devel mailing list by Dmitri Shmidt.

"The problem is in uart_pipe_isr() logic. It is never-ending (spinning)
after first time entrance: it is still processing RX but its nature doesn't allow any user
threads to get control."

https://lists.zephyrproject.org/pipermail/zephyr-devel/2017-December/008533.html
@erwango erwango self-assigned this Dec 6, 2017
@erwango erwango added platform: STM32 ST Micro STM32 area: UART Universal Asynchronous Receiver-Transmitter labels Dec 6, 2017
@erwango erwango added this to the v1.10.0 milestone Dec 6, 2017
erwango added a commit to erwango/zephyr that referenced this issue Dec 6, 2017
@erwango
drivers: serial: stm32: report only unmasked irq
6e45842 
Fix zephyrproject-rtos#5298
irq_is_pending function returned TXE/RXNE flag status
even if IRQ was masked, which led to enless loop
in uart_pipe when no TX was performed. Fix by reporting status only when
IRQ is unmasked.

Signed-Off-by: Erwan Gouriou <[email protected]>
@erwango erwango mentioned this issue Dec 6, 2017
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@pfalcon
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pfalcon commented Dec 6, 2017

Note that I saw similar effects in #42, and while working on irq-driven console in general: #49.

@erwango
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erwango commented Dec 6, 2017

while working on irq-driven console in general: #49.

Wouldn't it be because there is always a tx associated to rx in console case?
Hence TXE is set to 0 and while loop is exited.
I have been to reproduce issue by commenting out insert_char() in uart_console_isr, but no issue as is.

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pfalcon commented Dec 6, 2017

Sure, for the console case it was solved by following invariants later documented in #159 , #281. And I had to patch existing test in #42 to follow them too.

So, my points is that such problems were known, and there's an existing pattern how to resolve them. And my concern that this case wasn't resolved in a way to break previous cases. (I'm going to look at #5299 in detail, from the title, it sounds good).

galak pushed a commit that referenced this issue Dec 6, 2017
@erwango @galak
drivers: serial: stm32: report only unmasked irq
222bc60 
Fix #5298
irq_is_pending function returned TXE/RXNE flag status
even if IRQ was masked, which led to enless loop
in uart_pipe when no TX was performed. Fix by reporting status only when
IRQ is unmasked.

Signed-Off-by: Erwan Gouriou <[email protected]>
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