Recently, it was reported to me that you could provoke a double fault
panic with the NDISulator if you did "ifconfig ndis0 10.0.0.1/24," whereas "ifconfig ndis0 10.0.0.1/24 up" worked fine. The double fault was caused by the ifconfig thread running out of kernel stack space. (This was partly due to the NDIsulator using a couple of big buffers on the stack, but even after fixing that the double fault persisted.) It turns out that ndis_init() is called in both cases, but in the first case the code path passes through ieee80211_ioctl(), and it turns out ieee80211_ioctl() consumes a whopping 2400 bytes of stack space. Apparently, gcc -O2 causes the ieee80211_ioctl_get80211() routine to be inlined into ieee80211_ioctl(), and for some reason which I do not fully understand, this causes ieee80211_ioctl() to consume an extra 2K of stack space. To prevent this overly agressive optimization, ieee80211_ioctl_get80211() is now declared with __attribute__ ((noinline)). With this change, ieee80211_ioctl() now only reserves about 200 bytes of stack instead of 2400.
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2020-12-20 02:59:44 +00:00
svn path=/head/; revision=143110
@ -1224,6 +1224,25 @@ ieee80211_ioctl_getwmeparam(struct ieee80211com *ic, struct ieee80211req *ireq)
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return 0;
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}
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/*
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* When building the kernel with -O2 on the i386 architecture, gcc
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* seems to want to inline this function into ieee80211_ioctl()
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* (which is the only routine that calls it). When this happens,
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* ieee80211_ioctl() ends up consuming an additional 2K of stack
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* space. (Exactly why it needs so much is unclear.) The problem
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* is that it's possible for ieee80211_ioctl() to invoke other
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* routines (including driver init functions) which could then find
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* themselves perilously close to exhausting the stack.
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*
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* To avoid this, we deliberately prevent gcc from inlining this
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* routine. Another way to avoid this is to use less agressive
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* optimization when compiling this file (i.e. -O instead of -O2)
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* but special-casing the compilation of this one module in the
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* build system would be awkward.
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*/
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#ifdef __GNUC__
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__attribute__ ((noinline))
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#endif
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static int
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ieee80211_ioctl_get80211(struct ieee80211com *ic, u_long cmd, struct ieee80211req *ireq)
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{
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