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Subject[tip:x86/fpu] x86/fpu: Fix fpu__activate_fpstate_read() and update comments
Commit-ID:  4618e90965f272fe522f2af2523a60d0d4bc78f3
Gitweb: http://git.kernel.org/tip/4618e90965f272fe522f2af2523a60d0d4bc78f3
Author: Ingo Molnar <mingo@kernel.org>
AuthorDate: Sat, 23 Sep 2017 15:00:10 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 26 Sep 2017 09:41:09 +0200

x86/fpu: Fix fpu__activate_fpstate_read() and update comments

fpu__activate_fpstate_read() can be called for the current task
when coredumping - or for stopped tasks when ptrace-ing.

Implement this properly in the code and update the comments.

This also fixes an incorrect (but harmless) warning introduced by
one of the earlier patches.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-28-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/fpu/core.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 93103a9..afd3f2a 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -254,18 +254,21 @@ EXPORT_SYMBOL_GPL(fpu__activate_curr);
/*
* This function must be called before we read a task's fpstate.
*
- * If the task has not used the FPU before then initialize its
- * fpstate.
+ * There's two cases where this gets called:
+ *
+ * - for the current task (when coredumping), in which case we have
+ * to save the latest FPU registers into the fpstate,
+ *
+ * - or it's called for stopped tasks (ptrace), in which case the
+ * registers were already saved by the context-switch code when
+ * the task scheduled out - we only have to initialize the registers
+ * if they've never been initialized.
*
* If the task has used the FPU before then save it.
*/
void fpu__activate_fpstate_read(struct fpu *fpu)
{
- /*
- * If fpregs are active (in the current CPU), then
- * copy them to the fpstate:
- */
- if (fpu->fpstate_active) {
+ if (fpu == &current->thread.fpu) {
fpu__save(fpu);
} else {
if (!fpu->fpstate_active) {
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