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f702e62a19
Whenever serial_xmit fails to transmit a byte it adds a watch that would call it again when the "line" becomes ready. This results in a retry chain: serial_xmit -> add_watch -> serial_xmit Each chain is able to transmit one character, and for every character passed to serial by the guest driver a new chain is spawned. The problem lays with the fact that a new chain is spawned even when there is one already waiting on the watch. So there can be several retry chains waiting concurrently on one "line". Every chain tries to transmit current character, so character order is not messed up. But also every chain increases retry counter (tsr_retry). If there are enough concurrent chains this counter will hit MAX_XMIT_RETRY value and the character will be dropped. To reproduce this bug you need to feed serial output to some program consuming it slowly enough. A python script from bug #1335444 description is an example of such program. This commit changes retry logic in the following way to avoid concurrency: instead of spawning a new chain for each character being transmitted spawn only one and make it transmit characters until FIFO is empty. The change consists of two parts: - add a do {} while () loop in serial_xmit (diff is a bit erratic for this part, diff -w will show actual change), - do not call serial_xmit from serial_ioport_write if there is one waiting on the watch already. This should fix another issue causing bug #1335444. Signed-off-by: Kirill Batuzov <batuzovk@ispras.ru> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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| .. | ||
| cadence_uart.c | ||
| debugcon.c | ||
| digic-uart.c | ||
| escc.c | ||
| etraxfs_ser.c | ||
| exynos4210_uart.c | ||
| grlib_apbuart.c | ||
| imx_serial.c | ||
| ipoctal232.c | ||
| lm32_juart.c | ||
| lm32_uart.c | ||
| Makefile.objs | ||
| mcf_uart.c | ||
| milkymist-uart.c | ||
| omap_uart.c | ||
| parallel.c | ||
| pl011.c | ||
| sclpconsole-lm.c | ||
| sclpconsole.c | ||
| serial-isa.c | ||
| serial-pci.c | ||
| serial.c | ||
| sh_serial.c | ||
| spapr_vty.c | ||
| virtio-console.c | ||
| virtio-serial-bus.c | ||
| xen_console.c | ||
| xilinx_uartlite.c | ||