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Message-ID: <87vdr6z30e.fsf@pike.pond.sub.org> Date: Thu, 19 Feb 2009 19:37:53 +0100 From: Markus Armbruster <armbru@...hat.com> To: Ian Jackson <Ian.Jackson@...citrix.com> Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "xen-devel\@lists.xensource.com" <xen-devel@...ts.xensource.com>, Anders Kaseorg <andersk@....EDU> Subject: Re: [Xen-devel] Re: [PATCH] IRQ handling race and spurious IIR read in serial/8250.c Ian Jackson <Ian.Jackson@...citrix.com> writes: > I wrote: >> In drivers/serial/8250.c in Linux there are two bugs: >> 1. UART_BUG_TXEN can be spuriously set, due to an IRQ race >> 2. The workaround then applied by the kernel is itself buggy > > Markus Armbruster has also experienced this problem in a Xen > environment and has confirmed that my patch fixes it. Correct. > I think at the very least this change: > >> Proposed initial band-aid fix (against 2.6.28.4): >> >> Do not read IIR in serial8250_start_tx when UART_BUG_TXEN >> >> Reading the IIR clears some oustanding interrupts so it is not safe. >> Instead, simply transmit immediately if the buffer is empty without >> regard to IIR. >> >> Signed-off-by: Ian Jackson <ian.jackson@...citrix.com> > > should be made right away. > > Ian. Patch makes sense to me. Acked-by: Markus Armbruster <armbru@...hat.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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