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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
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>
-rw-r--r--include/asm-powerpc/current.h12
1 files changed, 11 insertions, 1 deletions
diff --git a/include/asm-powerpc/current.h b/include/asm-powerpc/current.h
index 1938d6abd25..b8708aedf92 100644
--- a/include/asm-powerpc/current.h
+++ b/include/asm-powerpc/current.h
@@ -14,7 +14,17 @@ struct task_struct;
#ifdef __powerpc64__
#include <asm/paca.h>
-#define current (get_paca()->__current)
+static inline struct task_struct *get_current(void)
+{
+ struct task_struct *task;
+
+ __asm__ __volatile__("ld %0,%1(13)"
+ : "=r" (task)
+ : "i" (offsetof(struct paca_struct, __current)));
+
+ return task;
+}
+#define current get_current()
#else