3.2-stable review patch. If anyone has any objections, please let me know.
------------------ From: Russell King <[email protected]> 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, stupid tool...] 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 <[email protected]> Signed-off-by: Russell King <[email protected]> Cc: Dominik Brodowski <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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"); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
