From e966eaeeb623f09975ef362c2866fae6f86844f9 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Tue, 12 Dec 2017 12:31:16 +0100 Subject: locking/lockdep: Remove the cross-release locking checks This code (CONFIG_LOCKDEP_CROSSRELEASE=y and CONFIG_LOCKDEP_COMPLETIONS=y), while it found a number of old bugs initially, was also causing too many false positives that caused people to disable lockdep - which is arguably a worse overall outcome. If we disable cross-release by default but keep the code upstream then in practice the most likely outcome is that we'll allow the situation to degrade gradually, by allowing entropy to introduce more and more false positives, until it overwhelms maintenance capacity. Another bad side effect was that people were trying to work around the false positives by uglifying/complicating unrelated code. There's a marked difference between annotating locking operations and uglifying good code just due to bad lock debugging code ... This gradual decrease in quality happened to a number of debugging facilities in the kernel, and lockdep is pretty complex already, so we cannot risk this outcome. Either cross-release checking can be done right with no false positives, or it should not be included in the upstream kernel. ( Note that it might make sense to maintain it out of tree and go through the false positives every now and then and see whether new bugs were introduced. ) Cc: Byungchul Park Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- lib/Kconfig.debug | 33 --------------------------------- 1 file changed, 33 deletions(-) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 947d3e2ed5c2..9d5b78aad4c5 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1099,8 +1099,6 @@ config PROVE_LOCKING select DEBUG_MUTEXES select DEBUG_RT_MUTEXES if RT_MUTEXES select DEBUG_LOCK_ALLOC - select LOCKDEP_CROSSRELEASE - select LOCKDEP_COMPLETIONS select TRACE_IRQFLAGS default n help @@ -1170,37 +1168,6 @@ config LOCK_STAT CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. (CONFIG_LOCKDEP defines "acquire" and "release" events.) -config LOCKDEP_CROSSRELEASE - bool - help - This makes lockdep work for crosslock which is a lock allowed to - be released in a different context from the acquisition context. - Normally a lock must be released in the context acquiring the lock. - However, relexing this constraint helps synchronization primitives - such as page locks or completions can use the lock correctness - detector, lockdep. - -config LOCKDEP_COMPLETIONS - bool - help - A deadlock caused by wait_for_completion() and complete() can be - detected by lockdep using crossrelease feature. - -config BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK - bool "Enable the boot parameter, crossrelease_fullstack" - depends on LOCKDEP_CROSSRELEASE - default n - help - The lockdep "cross-release" feature needs to record stack traces - (of calling functions) for all acquisitions, for eventual later - use during analysis. By default only a single caller is recorded, - because the unwind operation can be very expensive with deeper - stack chains. - - However a boot parameter, crossrelease_fullstack, was - introduced since sometimes deeper traces are required for full - analysis. This option turns on the boot parameter. - config DEBUG_LOCKDEP bool "Lock dependency engine debugging" depends on DEBUG_KERNEL && LOCKDEP -- cgit v1.2.3