uprobes: Shift ->readpage check from __copy_insn() to uprobe_register()
authorOleg Nesterov <oleg@redhat.com>
Mon, 19 May 2014 18:40:54 +0000 (20:40 +0200)
committerIngo Molnar <mingo@kernel.org>
Thu, 5 Jun 2014 10:30:07 +0000 (12:30 +0200)
copy_insn() fails with -EIO if ->readpage == NULL, but this error
is not propagated unless uprobe_register() path finds ->mm which
already mmaps this file. In this case (say) "perf record" does not
actually install the probe, but the user can't know about this.

Move this check into uprobe_register() so that this problem can be
detected earlier and reported to user.

Note: this is still not perfect,

- copy_insn() and arch_uprobe_analyze_insn() should be called
  by uprobe_register() but this is not simple, we need vm_file
  for read_mapping_page() (although perhaps we can pass NULL),
  and we need ->mm for is_64bit_mm() (although this logic is
  broken anyway).

- uprobe_register() should be called by create_trace_uprobe(),
  not by probe_event_enable(), so that an error can be detected
  at "perf probe -x" time. This also needs more changes in the
  core uprobe code, uprobe register/unregister interface was
  poorly designed from the very beginning.

Reported-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140519184054.GA6750@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
kernel/events/uprobes.c

index 3b02c72..c56b13e 100644 (file)
@@ -536,9 +536,6 @@ static int __copy_insn(struct address_space *mapping, struct file *filp,
                        void *insn, int nbytes, loff_t offset)
 {
        struct page *page;
-
-       if (!mapping->a_ops->readpage)
-               return -EIO;
        /*
         * Ensure that the page that has the original instruction is
         * populated and in page-cache.
@@ -879,6 +876,9 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
        if (!uc->handler && !uc->ret_handler)
                return -EINVAL;
 
+       /* copy_insn()->read_mapping_page() needs ->readpage() */
+       if (!inode->i_mapping->a_ops->readpage)
+               return -EIO;
        /* Racy, just to catch the obvious mistakes */
        if (offset > i_size_read(inode))
                return -EINVAL;