uprobes: Fix prepare_uprobe() race with itself
commit4710f05fd146d4739e57a8832a3abc5bd3bf0997
authorOleg Nesterov <oleg@redhat.com>
Sun, 30 Sep 2012 18:31:41 +0000 (30 20:31 +0200)
committerOleg Nesterov <oleg@redhat.com>
Sun, 7 Oct 2012 19:19:43 +0000 (7 21:19 +0200)
tree459f64b5243d621c85b34abf90e3892cca69e502
parentcb9a19fe4aa51afa34786bd383e6614fa0083d58
uprobes: Fix prepare_uprobe() race with itself

install_breakpoint() is called under mm->mmap_sem, this protects
set_swbp() but not prepare_uprobe(). Two or more different tasks
can call install_breakpoint()->prepare_uprobe() at the same time,
this leads to numerous problems if UPROBE_COPY_INSN is not set.

Just for example, the second copy_insn() can corrupt the already
analyzed/fixuped uprobe->arch.insn and race with handle_swbp().

This patch simply adds uprobe->copy_mutex to serialize this code.
We could probably reuse ->consumer_rwsem, but this would mean that
consumer->handler() can not use mm->mmap_sem, not good.

Note: this is another temporary ugly hack until we move this logic
into uprobe_register().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
kernel/events/uprobes.c