ptrace.c change in 2.6.15 (?) breaks code for listing threads

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



I was recently informed by a user of google-perftools.sf.net, that current Linux kernels no longer allow perftools (and related code, such as goog-coredumper.sf.net) to list threads in a running application.

I tracked the problem down to this changelist:

--- 5b8dd98a230e442c1ec46adc968acb60dfdb74ae
+++ b88d4186cd7ac2733c3adf231d5b4daa4e14b0a9
@@ -155,7 +155,7 @@ int ptrace_attach(struct task_struct *ta
 	retval = -EPERM;
 	if (task->pid <= 1)
 		goto bad;
-	if (task == current)
+	if (task->tgid == current->tgid)
 		goto bad;
 	/* the same process cannot be attached many times */
 	if (task->ptrace & PT_PTRACED)

I believe, if I interpret the data on kernel.org correctly, this change was made by Linus and shipped with 2.6.15.

Both perftools and coredumper need to locate all threads in the active application in order to work. As libpthread has had changing and poorly documented APIs to get this information, and as our intent is to support all kernel versions and all libc versions, we resorted to ptracing any process that is suspected to be one of our threads in order to determine if it actually is. This has the added benefit of finding *all* threads (including ones not managed by libpthread) and of temporarily suspending them, so that we have a stable memory image that we can inspect. Think of both tools as something like a lightweight in-process debugger.

Obviously, special care has to be taken to not ptrace our own thread, and to avoid any library calls that could deadlock.

Before the patch, attaching ptrace to my own threads was a valid operation. With this new patch, I can no longer do that.

I'd be happy to consider alternative approaches (which might be cleaner, anyway) to list and suspend all of the threads in my application. But before I do that I would like to ask if there is any chance the restrictions imposed with this patch could be lifted. It would certainly make my life easier if Linux continued to allow processes to ptrace themselves -- as far as I have been able to test it, this feature has been working ever since Linux first supported threads and only broke very recently.


Markus

P.S.: I usually read LKML as archived on the web, so please cc me on any responses, if you want me to see your answer quickly. Thanks.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux