possible bug in pci/hotplug/pciehp_core.c in linux-2.6.19

[Philip Guo <pg@cs.stanford.edu>]

Hi,

I am a graduate student working on finding bugs in Linux drivers using 
an automated research tool.  I think I've found a possible bug in 
pci/hotplug/pciehp_core.c, and I'd appreciate it if you could 
confirm/disconfirm it.

This code is in 2.6.19, but I just checked on 2.6.20.1, and this same 
problem seems to still be present.

Thanks,
Philip

---
One thread seems to deadlock itself by calling down() on a semaphore
initialized to locked.

pci/hotplug/pciehp_core.c:

Start at pcied_init() -

static int __init pcied_init(void)
{
     int retval = 0;

#ifdef CONFIG_HOTPLUG_PCI_PCIE_POLL_EVENT_MODE
     pciehp_poll_mode = 1;
#endif

     retval = pcie_start_thread(); <-- [this returns an error]
     if (retval)
         goto error_hpc_init;
[...]

error_hpc_init:
     if (retval) { <-- [true]
         pciehp_event_stop_thread(); <-- [calling this will deadlock - 
see code snippet at the end]
     };

     return retval;
}


static int pcie_start_thread(void)
{
     int retval = 0;
     retval = pciehp_event_start_thread(); <-- [call this]
     if (retval) { <-- [take failed branch]
         return retval;
     }
     return retval;
}


pci/hotplug/pciehp_ctrl.c:

static struct semaphore event_exit; /* guard ensure thread has exited 
before calling it quits */

int pciehp_event_start_thread(void)
{
     int pid;

     /* initialize our semaphores */
     init_MUTEX_LOCKED(&event_exit); <-- [event_exit init to LOCKED]
     event_finished=0;

     init_MUTEX_LOCKED(&event_semaphore);
     pid = kernel_thread(event_thread, NULL, 0); <-- [this fails]

     if (pid < 0) { <-- [take this branch because kernel_thread failed]
         err ("Can't start up our event thread\n");
         return -1; <-- [return error]
     }
     return 0;
}

void pciehp_event_stop_thread(void)
{
     event_finished = 1;
     up(&event_semaphore);
     down(&event_exit); <-- [this is called from the end of pcied_init() 
on a LOCKED semaphore, so deadlock]
}


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