[PATCH 0/4 v3] Use static buffers to log from driver signal handlers

[Mark Kettenis]

> From: Daniel Kurtz
> Date: Fri,  5 Aug 2011 15:09:57 +0800
> 
> For Version 3:
>  * 0001: Make cleaner and faster per Guillem Jover review comments.
>  * 0002: Make slightly faster and fix some comments.
> 
> Back in the bad old days, using xf86Msg() from a signal handler was a
> big no-no, as it would deadlock the system on malloc when the prefix is
> prepended.  Thus, only X_NONE messages could be used to bypass this.
> However, LogVWrite limits to 1024 bytes anyway, so a patch was made to
> eliminate malloc in LogVMessageVerb().

I think this diff is misguided.  LogVMessageVerb() still calls
snprintf(), which is *not* async-signal-safe.  And, no, this is not a
theoretical issue.  In many C libraries the code to print
floating-point numbers is based on gdtoa, which calls malloc().

> However, input driver messages these days go through xf86VIDrvMsgVerb(),
> which does its own asprintf()/mallocs() to prefix the driver and device
> names, reintroducing the same old no-no.

The input drivers should really not try to print messages from signal
handlers.