On 05.11.2019 22:08, m...@netbsd.org wrote: > On Tue, Nov 05, 2019 at 09:01:06PM +0000, m...@netbsd.org wrote: >> On Tue, Nov 05, 2019 at 08:19:18PM +0000, Maxime Villard wrote: >>> Module Name: src >>> Committed By: maxv >>> Date: Tue Nov 5 20:19:18 UTC 2019 >>> >>> Modified Files: >>> src/share/mk: bsd.sys.mk >>> src/sys/arch/amd64/amd64: machdep.c mptramp.S >>> src/sys/arch/amd64/conf: GENERIC Makefile.amd64 >>> src/sys/arch/x86/x86: cpu.c >>> src/sys/conf: files >>> src/sys/kern: files.kern >>> src/sys/lib/libkern: libkern.h >>> src/sys/sys: atomic.h bus_proto.h cdefs.h systm.h >>> Added Files: >>> src/sys/arch/amd64/include: csan.h >>> src/sys/kern: subr_csan.c >>> src/sys/sys: csan.h >>> >>> Log Message: >>> Add Kernel Concurrency Sanitizer (kCSan) support. This sanitizer allows us >>> to detect race conditions at runtime. It is a variation of TSan that is >>> easy to implement and more suited to kernel internals, albeit theoretically >>> less precise than TSan's happens-before. >>> >>> We do basically two things: >>> >>> - On every KCSAN_NACCESSES (=2000) memory accesses, we create a cell >>> describing the access, and delay the calling CPU (10ms). >>> >>> - On all memory accesses, we verify if the memory we're reading/writing >>> is referenced in a cell already. >>> >>> The combination of the two means that, if for example cpu0 does a read that >>> is selected and cpu1 does a write at the same address, kCSan will fire, >>> because cpu1's write collides with cpu0's read cell. >>> >>> The coverage of the instrumentation is the same as that of kASan. Also, the >>> code is organized in a way similar to kASan, so it is easy to add support >>> for more architectures than amd64. kCSan is compatible with KCOV. >>> >>> Reviewed by Kamil. >>> >> >> I don't understand how you can distinguish a race from this condition: >> >> CPU0 CPU1 >> >> >> mutex_enter >> write (recorded to cell) >> mutex_exit >> >> read (checked against record) >> >> Which is legitimate.^W > would be if I used a mutex on CPU0, but the point still stands. :-) >
This sanitizer checks whether a violation is occurring now. TSan would check whether it is possible and triggers false positives in the kernel.
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