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authorHugh Dickins <hugh@veritas.com>2006-10-31 18:39:31 +0000
committerPaul Mackerras <paulus@samba.org>2006-11-01 14:52:48 +1100
commit5fe8e8b88e68e517637e3f8287f1fee89e2d9252 (patch)
tree5b7d1878e9d16107d7c8fcfa0d866d660372161d /include/asm-powerpc/io.h
parent302439d2167e0f1e01a6480ac40c06063f4e16a1 (diff)
[POWERPC] Make current preempt-safe
Repeated -j20 kernel builds on a G5 Quad running an SMP PREEMPT kernel would often collapse within a day, some exec failing with "Bad address". In each case examined, load_elf_binary was doing a kernel_read, but generic_file_aio_read's access_ok saw current->thread.fs.seg as USER_DS instead of KERNEL_DS. objdump of filemap.o shows gcc 4.1.0 emitting "mr r5,r13 ... ld r9,416(r5)" here for get_paca()->__current, instead of the expected and much more usual "ld r9,416(r13)"; I've seen other gcc4s do the same, but perhaps not gcc3s. So, if the task is preempted and rescheduled on a different cpu in between the mr and the ld, r5 will be looking at a different paca_struct from the one it's now on, pick up the wrong __current, and perhaps the wrong seg. Presumably much worse could happen elsewhere, though that split is rare. Other architectures appear to be safe (x86_64's read_pda is more limiting than get_paca), but ppc64 needs to force "current" into one instruction. Signed-off-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Paul Mackerras <paulus@samba.org>
Diffstat (limited to 'include/asm-powerpc/io.h')
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