uprobes: Teach handle_swbp() to rely on "is_swbp" rather than uprobes_srcu
commit56bb4cf6475d702d2fb00fc641aa6441097c0330
authorOleg Nesterov <oleg@redhat.com>
Tue, 29 May 2012 19:29:47 +0000 (29 21:29 +0200)
committerIngo Molnar <mingo@kernel.org>
Wed, 6 Jun 2012 15:22:03 +0000 (6 17:22 +0200)
tree0be90e9cdb9d998e9ca795f12eb530b397435844
parent77fc4af1b59d12ab3b1467adf0a5204806853123
uprobes: Teach handle_swbp() to rely on "is_swbp" rather than uprobes_srcu

Currently handle_swbp() assumes that it can't race with
unregister, so it roughly does:

if (find_uprobe(vaddr))
process_uprobe();
else
send_sig(SIGTRAP);

This relies on the not-really-working uprobes_srcu code we are
going to remove, see the next patch.

With this patch we rely on the result of
is_swbp_at_addr(bp_vaddr) if find_uprobe() fails.

If is_swbp == 1, then we hit the normal int3, we should send
SIGTRAP.

If is_swbp == 0, we raced with uprobe_unregister(), we simply
restart this insn again.

The "difficult" case is is_swbp == -EFAULT, when we can't read
this memory. In this case I think we should restart too, and
this is more correct compared to the current code which sends
SIGTRAP.

Ignoring ENOMEM/etc from get_user_pages(), this can only happen
if another thread unmaps this memory before find_active_uprobe()
takes mmap_sem. It would be better to pretend it was unmapped
before this insn was executed, restart, and get SIGSEGV.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120529192947.GF8057@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/events/uprobes.c