64-bit little endian semaphore bug
In the 64-bit kernel, the semaphore structure (like the 32-bit kernel) has waking and count fields swizzled so they line up the same in a 64-bit double word for either endian. However, the semaphore-helper.h function waking_non_zero_interruptible still has specialized code for little-endian manipulation of the fields as though they are swapped.
Patch is attached, and fixes a pipe deadlock I was seeing (both the reader and writer were down'ing the semaphore).
patch is against 2.5, but should be clean against 2.4 also.
Kip
Index: include/asm-mips64/semaphore-helper.h
===================================================================
RCS file: /home/cvs/linux/include/asm-mips64/semaphore-helper.h,v retrieving revision 1.10
asm-mips64/semaphore-helper.h +0 -34
@@ -66,8 +66,6 @@ {long ret, tmp; -#ifdef __MIPSEB__ - __asm__ __volatile__(".set\tpush\t\t\t# waking_non_zero_interruptible\n\t" ".set\tnoat\n\t"
@@ -87,38 +85,6 @@ ".set\tpop" : "=&r" (ret), "=&r" (tmp), "=m" (*sem) : "r" (signal_pending(tsk)), "i" (-EINTR)); - -#elif defined(__MIPSEL__) - - __asm__ __volatile__( -".set\tpush\t\t\t# waking_non_zero_interruptible\n\t" -".set\t noat\n" -"0:\tlld\t%1, %2\n\t" -"li\t%0, 0\n\t" -"blez\t%1, 1f\n\t" -"dli\t$1, 0x0000000100000000\n\t" -"dsubu\t%1, %1, $1\n\t" -"li\t%0, 1\n\t" -"b\t2f\n" -"1:\tbeqz\t%3, 2f\n\t" -"li\t%0, %4\n\t" -/* -* It would be nice to assume that sem->count -* is != -1, but we will guard against that case -*/ -"daddiu\t$1, %1, 1\n\t" -"dsll32\t$1, $1, 0\n\t" -"dsrl32\t$1, $1, 0\n\t" -"dsrl32\t%1, %1, 0\n\t" -"dsll32\t%1, %1, 0\n\t" -"or\t%1, %1, $1\n" -"2:\tscd\t%1, %2\n\t" -"beqz\t %1, 0b\n\t" -".set\tpop" - :"=&r" (ret),"=&r" (tmp),"=m" (*sem) - :"r" (signal_pending (tsk)),"i" (-EINTR )); - -#endif return ret; }
Quoted 10 lines · Kip Walker
In the 64-bit kernel, the semaphore structure (like the 32-bit kernel) has waking and count fields swizzled so they line up the same in a 64-bit double word for either endian. However, the
semaphore-helper.hfunctionwaking_non_zero_interruptiblestill has specialized code for little-endian manipulation of the fields as though they are swapped.Patch is attached, and fixes a pipe deadlock I was seeing (both the reader and writer were down'ing the semaphore).
patch is against 2.5, but should be clean against 2.4 also.
Patch is ok. I tweaked it slightly to make the 2.4 and 2.5 versions identical.
General request to everybody - cc me on all patches that you wish to submit even if you're posting them to some list.
Ralf