[patch 39/55] pcmcia: fix socket refcount decrementing on each resume

[Greg KH <gregkh@linuxfoundation.org>]

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Russell King <rmk+kernel@arm.linux.org.uk>

commit 025e4ab3db07fcbf62c01e4f30d1012234beb980 upstream.

This fixes a memory-corrupting bug: not only does it cause the warning,
but as a result of dropping the refcount to zero, it causes the
pcmcia_socket0 device structure to be freed while it still has
references, causing slab caches corruption.  A fatal oops quickly
follows this warning - often even just a 'dmesg' following the warning
causes the kernel to oops.

While testing suspend/resume on an ARM device with PCMCIA support, and a
CF card inserted, I found that after five suspend and resumes, the
kernel would complain, and shortly die after with slab corruption.

  WARNING: at include/linux/kref.h:41 kobject_get+0x28/0x50()

As the message doesn't give a clue about which kobject, and the built-in
debugging in drivers/base/power/main.c happens too late, this was added
right before each get_device():

  printk("%s: %p [%s] %u\n", __func__, dev, kobject_name(&dev->kobj), atomic_read(&dev->kobj.kref.refcount));

and on the 3rd s2ram cycle, the following behaviour observed:

On the 3rd suspend/resume cycle:

  dpm_prepare: c1a0d998 [pcmcia_socket0] 3
  dpm_suspend: c1a0d998 [pcmcia_socket0] 3
  dpm_suspend_noirq: c1a0d998 [pcmcia_socket0] 3
  dpm_resume_noirq: c1a0d998 [pcmcia_socket0] 3
  dpm_resume: c1a0d998 [pcmcia_socket0] 3
  dpm_complete: c1a0d998 [pcmcia_socket0] 2

4th:

  dpm_prepare: c1a0d998 [pcmcia_socket0] 2
  dpm_suspend: c1a0d998 [pcmcia_socket0] 2
  dpm_suspend_noirq: c1a0d998 [pcmcia_socket0] 2
  dpm_resume_noirq: c1a0d998 [pcmcia_socket0] 2
  dpm_resume: c1a0d998 [pcmcia_socket0] 2
  dpm_complete: c1a0d998 [pcmcia_socket0] 1

5th:

  dpm_prepare: c1a0d998 [pcmcia_socket0] 1
  dpm_suspend: c1a0d998 [pcmcia_socket0] 1
  dpm_suspend_noirq: c1a0d998 [pcmcia_socket0] 1
  dpm_resume_noirq: c1a0d998 [pcmcia_socket0] 1
  dpm_resume: c1a0d998 [pcmcia_socket0] 1
  dpm_complete: c1a0d998 [pcmcia_socket0] 0
  ------------[ cut here ]------------
  WARNING: at include/linux/kref.h:41 kobject_get+0x28/0x50()
  Modules linked in: ucb1x00_core
  Backtrace:
  [<c0212090>] (dump_backtrace+0x0/0x110) from [<c04799dc>] (dump_stack+0x18/0x1c)
  [<c04799c4>] (dump_stack+0x0/0x1c) from [<c021cba0>] (warn_slowpath_common+0x50/0x68)
  [<c021cb50>] (warn_slowpath_common+0x0/0x68) from [<c021cbdc>] (warn_slowpath_null+0x24/0x28)
  [<c021cbb8>] (warn_slowpath_null+0x0/0x28) from [<c0335374>] (kobject_get+0x28/0x50)
  [<c033534c>] (kobject_get+0x0/0x50) from [<c03804f4>] (get_device+0x1c/0x24)
  [<c0388c90>] (dpm_complete+0x0/0x1a0) from [<c0389cc0>] (dpm_resume_end+0x1c/0x20)
  ...

[changelog edited to make quilt mail happy...]

As can be seen, the original function called pcmcia_get_socket() and
pcmcia_put_socket() around the guts, whereas the replacement code
calls pcmcia_put_socket() only in one path.  This creates an imbalance
in the refcounting.

Testing with pcmcia_put_socket() put removed shows that the bug is gone:

  dpm_suspend: c1a10998 [pcmcia_socket0] 5
  dpm_suspend_noirq: c1a10998 [pcmcia_socket0] 5
  dpm_resume_noirq: c1a10998 [pcmcia_socket0] 5
  dpm_resume: c1a10998 [pcmcia_socket0] 5
  dpm_complete: c1a10998 [pcmcia_socket0] 5

Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/pcmcia/ds.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/pcmcia/ds.c
+++ b/drivers/pcmcia/ds.c
@@ -1269,10 +1269,8 @@ static int pcmcia_bus_add(struct pcmcia_
 
 static int pcmcia_bus_early_resume(struct pcmcia_socket *skt)
 {
-	if (!verify_cis_cache(skt)) {
-		pcmcia_put_socket(skt);
+	if (!verify_cis_cache(skt))
 		return 0;
-	}
 
 	dev_dbg(&skt->dev, "cis mismatch - different card\n");