Hello,
This patch fixes a deadlock problem of the m32r SMP kernel.
In the m32r kernel, sys_tas() system call is provided as a test-and-set
function for userspace, for backward compatibility.
In some multi-threading application program, deadlocks were rarely caused
at sys_tas() funcion.
Such a deadlock was caused due to a collision of __pthread_lock() and
__pthread_unlock() operations.
The "tas" syscall is repeatedly called by pthread_mutex_lock() to get
a lock, while a lock variable's value is not 0.
On the other hand, pthead_mutex_unlock() sets the lock variable to 0
for unlocking.
In the previous implementation of sys_tas() routine, there was a possibility
that a unlock operation was ignored in the following case:
- Assume a lock variable (*addr) was equal to 1 before sys_tas() execution.
- __pthread_unlock() operation is executed by the other processor
and the lock variable (*addr) is set to 0, between a read operation
("oldval = *addr;") and the following write operation ("*addr = 1;")
during a execution of sys_tas().
In this case, the following write operation ("*addr = 1;") overwrites
the __pthread_unlock() result, and sys_tas() fails to get a lock in the
next turn and after that.
According to the attatched patch, sys_tas() returns 0 value in the next turn
and deadlocks never happen.
Signed-off-by: Hitoshi Yamamoto <[email protected]>
Signed-off-by: Hirokazu Takata <[email protected]>
---
arch/m32r/kernel/sys_m32r.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
Index: linux-2.6.14-mm1/arch/m32r/kernel/sys_m32r.c
===================================================================
--- linux-2.6.14-mm1.orig/arch/m32r/kernel/sys_m32r.c 2005-11-07 19:31:23.404878304 +0900
+++ linux-2.6.14-mm1/arch/m32r/kernel/sys_m32r.c 2005-11-07 19:33:04.991434800 +0900
@@ -41,7 +41,8 @@ asmlinkage int sys_tas(int *addr)
return -EFAULT;
local_irq_save(flags);
oldval = *addr;
- *addr = 1;
+ if (!oldval)
+ *addr = 1;
local_irq_restore(flags);
return oldval;
}
@@ -59,7 +60,8 @@ asmlinkage int sys_tas(int *addr)
_raw_spin_lock(&tas_lock);
oldval = *addr;
- *addr = 1;
+ if (!oldval)
+ *addr = 1;
_raw_spin_unlock(&tas_lock);
return oldval;
--
Hirokazu Takata <[email protected]>
Linux/M32R Project: http://www.linux-m32r.org/
-
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]
