From de801de139ba2a2f2c74393ea00a321477ecc0dc Mon Sep 17 00:00:00 2001 From: Jimi Xenidis Date: Tue, 28 Feb 2012 13:27:07 +0000 Subject: [PATCH] powerpc/icswx: Fix race condition with IPI setting ACOP There is a race where a thread causes a coprocessor type to be valid in its own ACOP _and_ in the current context, but it does not propagate to the ACOP register of other threads in time for them to use it. The original code tries to solve this by sending an IPI to all threads on the system, which is heavy handed, but unfortunately still provides a window where the icswx is issued by other threads and the ACOP is not up to date. This patch detects that the ACOP DSI fault was a "false positive" and syncs the ACOP and causes the icswx to be replayed. Signed-off-by: Jimi Xenidis Cc: Anton Blanchard Cc: Benjamin Herrenschmidt Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/mm/icswx.c | 23 +++++++++++++++++++++-- arch/powerpc/mm/icswx.h | 6 ++++++ 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/mm/icswx.c b/arch/powerpc/mm/icswx.c index 5d9a59eaad9..8cdbd8634a5 100644 --- a/arch/powerpc/mm/icswx.c +++ b/arch/powerpc/mm/icswx.c @@ -163,7 +163,7 @@ EXPORT_SYMBOL_GPL(drop_cop); static int acop_use_cop(int ct) { - /* todo */ + /* There is no alternate policy, yet */ return -1; } @@ -227,11 +227,30 @@ int acop_handle_fault(struct pt_regs *regs, unsigned long address, ct = (ccw >> 16) & 0x3f; } + /* + * We could be here because another thread has enabled acop + * but the ACOP register has yet to be updated. + * + * This should have been taken care of by the IPI to sync all + * the threads (see smp_call_function(sync_cop, mm, 1)), but + * that could take forever if there are a significant amount + * of threads. + * + * Given the number of threads on some of these systems, + * perhaps this is the best way to sync ACOP rather than whack + * every thread with an IPI. + */ + if ((acop_copro_type_bit(ct) & current->active_mm->context.acop) != 0) { + sync_cop(current->active_mm); + return 0; + } + + /* check for alternate policy */ if (!acop_use_cop(ct)) return 0; /* at this point the CT is unknown to the system */ - pr_warn("%s[%d]: Coprocessor %d is unavailable", + pr_warn("%s[%d]: Coprocessor %d is unavailable\n", current->comm, current->pid, ct); /* get inst if we don't already have it */ diff --git a/arch/powerpc/mm/icswx.h b/arch/powerpc/mm/icswx.h index 42176bd0884..6dedc08e62c 100644 --- a/arch/powerpc/mm/icswx.h +++ b/arch/powerpc/mm/icswx.h @@ -59,4 +59,10 @@ extern void free_cop_pid(int free_pid); extern int acop_handle_fault(struct pt_regs *regs, unsigned long address, unsigned long error_code); + +static inline u64 acop_copro_type_bit(unsigned int type) +{ + return 1ULL << (63 - type); +} + #endif /* !_ARCH_POWERPC_MM_ICSWX_H_ */ -- 2.39.5