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authorMichael Neuling <mikey@neuling.org>2014-03-03 14:21:40 +1100
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2014-03-07 13:50:15 +1100
commit621b5060e823301d0cba4cb52a7ee3491922d291 (patch)
tree02f4db8401066a844e4851f9e1e313d22331d13d
parente0cf957614976896111e676e5134ac98ee227d3d (diff)
downloadlinux-621b5060e823301d0cba4cb52a7ee3491922d291.tar.gz
powerpc/tm: Fix crash when forking inside a transaction
When we fork/clone we currently don't copy any of the TM state to the new thread. This results in a TM bad thing (program check) when the new process is switched in as the kernel does a tmrechkpt with TEXASR FS not set. Also, since R1 is from userspace, we trigger the bad kernel stack pointer detection. So we end up with something like this: Bad kernel stack pointer 0 at c0000000000404fc cpu 0x2: Vector: 700 (Program Check) at [c00000003ffefd40] pc: c0000000000404fc: restore_gprs+0xc0/0x148 lr: 0000000000000000 sp: 0 msr: 9000000100201030 current = 0xc000001dd1417c30 paca = 0xc00000000fe00800 softe: 0 irq_happened: 0x01 pid = 0, comm = swapper/2 WARNING: exception is not recoverable, can't continue The below fixes this by flushing the TM state before we copy the task_struct to the clone. To do this we go through the tmreclaim patch, which removes the checkpointed registers from the CPU and transitions the CPU out of TM suspend mode. Hence we need to call tmrechkpt after to restore the checkpointed state and the TM mode for the current task. To make this fail from userspace is simply: tbegin li r0, 2 sc <boom> Kudos to Adhemerval Zanella Neto for finding this. Signed-off-by: Michael Neuling <mikey@neuling.org> cc: Adhemerval Zanella Neto <azanella@br.ibm.com> cc: stable@vger.kernel.org Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
-rw-r--r--arch/powerpc/kernel/process.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 8d4c247f1738..af064d28b365 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1048,6 +1048,15 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
flush_altivec_to_thread(src);
flush_vsx_to_thread(src);
flush_spe_to_thread(src);
+ /*
+ * Flush TM state out so we can copy it. __switch_to_tm() does this
+ * flush but it removes the checkpointed state from the current CPU and
+ * transitions the CPU out of TM mode. Hence we need to call
+ * tm_recheckpoint_new_task() (on the same task) to restore the
+ * checkpointed state back and the TM mode.
+ */
+ __switch_to_tm(src);
+ tm_recheckpoint_new_task(src);
*dst = *src;