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46aa7b3939
A race condition in rwsem_is_locked() was fixed in Linux 2.6.33 and the fix was backported to RHEL5 as of kernel 2.6.18-190.el5. Details can be found here: https://bugzilla.redhat.com/show_bug.cgi?id=526092 The race condition was fixed in the kernel by acquiring the semaphore's wait_lock inside rwsem_is_locked(). The SPL worked around the race condition by acquiring the wait_lock before calling that function, but with the fix in place it must not do that. This commit implements an autoconf test to detect whether the fixed version of rwsem_is_locked() is present. The previous version of rwsem_is_locked() was an inline static function while the new version is exported as a symbol which we can check for in module.symvers. Depending on the result we correctly implement the needed compatibility macros for proper spinlock handling. Finally, we do the right thing with spin locks in RW_*_HELD() by using the new compatibility macros. We only only acquire the semaphore's wait_lock if it is calling a rwsem_is_locked() that does not itself try to acquire the lock. Some new overhead and a small harmless race is introduced by this change. This is because RW_READ_HELD() and RW_WRITE_HELD() now acquire and release the wait_lock twice: once for the call to rwsem_is_locked() and once for the call to rw_owner(). This can't be avoided if calling a rwsem_is_locked() that takes the wait_lock, as it will in more recent kernels. The other case which only occurs in legacy kernels could be optimized by taking the lock only once, as was done prior to this commit. However, I decided that the performance gain probably wasn't significant enough to justify the messy special cases required. The function spl_rw_get_owner() was only used to enable the afore-mentioned optimization. Since it is no longer used, I removed it. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> |
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| fs | ||
| linux | ||
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| sharefs | ||
| sys | ||
| util | ||
| vm | ||
| .gitignore | ||
| Makefile.am | ||
| Makefile.in | ||
| spl-ctl.h | ||
| spl-debug.h | ||
| spl-device.h | ||
| spl-trace.h | ||
| splat-ctl.h | ||
| strings.h | ||
| unistd.h | ||