| Message ID | 20190711234401.220336-1-joel@joelfernandes.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Harden list_for_each_entry_rcu() and family | expand |
On Thu, Jul 11, 2019 at 07:43:55PM -0400, Joel Fernandes (Google) wrote: > Hi, > This series aims to provide lockdep checking to RCU list macros. > > RCU has a number of primitives for "consumption" of an RCU protected pointer. > Most of the time, these consumers make sure that such accesses are under a RCU > reader-section (such as rcu_dereference{,sched,bh} or under a lock, such as > with rcu_dereference_protected()). > > However, there are other ways to consume RCU pointers, such as by > list_for_each_entry_rcu or hlist_for_each_enry_rcu. Unlike the rcu_dereference > family, these consumers do no lockdep checking at all. And with the growing > number of RCU list uses (1000+), it is possible for bugs to creep in and go > unnoticed which lockdep checks can catch. I forgot to add in my cover letter, I have kept this option default-disabled under a new config: CONFIG_PROVE_RCU_LIST. This is so that until all users are converted to pass the optional argument, we should keep the check disabled. There are about a 1000 or so users and it is not possible to pass in the optional lockdep expression in a single series since it is done on a case-by-case basis. I did convert a few users in this series itself. Also, I plans to update the RCU documentation as well which I will do, but do review this series and thank you!
Hi, This series aims to provide lockdep checking to RCU list macros. RCU has a number of primitives for "consumption" of an RCU protected pointer. Most of the time, these consumers make sure that such accesses are under a RCU reader-section (such as rcu_dereference{,sched,bh} or under a lock, such as with rcu_dereference_protected()). However, there are other ways to consume RCU pointers, such as by list_for_each_entry_rcu or hlist_for_each_enry_rcu. Unlike the rcu_dereference family, these consumers do no lockdep checking at all. And with the growing number of RCU list uses (1000+), it is possible for bugs to creep in and go unnoticed which lockdep checks can catch. Since RCU consolidation efforts last year, the different traditional RCU flavors (preempt, bh, sched) are all consolidated. In other words, any of these flavors can cause a reader section to occur and all of them must cease before the reader section is considered to be unlocked. Thanks to this, we can generically check if we are in an RCU reader. This is what patch 1 does. Note that the list_for_each_entry_rcu and family are different from the rcu_dereference family in that, there is no _bh or _sched version of this macro. They are used under many different RCU reader flavors, and also SRCU. Patch 1 adds a new internal function rcu_read_lock_any_held() which checks if any reader section is active at all, when these macros are called. If no reader section exists, then the optional fourth argument to list_for_each_entry_rcu() can be a lockdep expression which is evaluated (similar to how rcu_dereference_check() works). If no lockdep expression is passed, and we are not in a reader, then a splat occurs. Just take off the lockdep expression after applying the patches, by using the following diff and see what happens: +++ b/arch/x86/pci/mmconfig-shared.c @@ -55,7 +55,7 @@ static void list_add_sorted(struct pci_mmcfg_region *new) struct pci_mmcfg_region *cfg; /* keep list sorted by segment and starting bus number */ - list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list, pci_mmcfg_lock_held()) { + list_for_each_entry_rcu(cfg, &pci_mmcfg_list, list) { The optional argument trick to list_for_each_entry_rcu() can also be used in the future to possibly remove rcu_dereference_{,bh,sched}_protected() API and we can pass an optional lockdep expression to rcu_dereference() itself. Thus eliminating 3 more RCU APIs. Note that some list macro wrappers already do their own lockdep checking in the caller side. These can be eliminated in favor of the built-in lockdep checking in the list macro that this series adds. For example, workqueue code has a assert_rcu_or_wq_mutex() function which is called in for_each_wq(). This series replaces that in favor of the built-in check. Also in the future, we can extend these checks to list_entry_rcu() and other list macros as well, if needed. Joel Fernandes (Google) (6): rcu: Add support for consolidated-RCU reader checking ipv4: add lockdep condition to fix for_each_entry driver/core: Convert to use built-in RCU list checking workqueue: Convert for_each_wq to use built-in list check x86/pci: Pass lockdep condition to pcm_mmcfg_list iterator acpi: Use built-in RCU list checking for acpi_ioremaps list arch/x86/pci/mmconfig-shared.c | 5 +++-- drivers/acpi/osl.c | 6 ++++-- drivers/base/base.h | 1 + drivers/base/core.c | 10 ++++++++++ drivers/base/power/runtime.c | 15 ++++++++++----- include/linux/rculist.h | 29 ++++++++++++++++++++++++----- include/linux/rcupdate.h | 7 +++++++ kernel/rcu/Kconfig.debug | 11 +++++++++++ kernel/rcu/update.c | 26 ++++++++++++++++++++++++++ kernel/workqueue.c | 5 ++--- net/ipv4/fib_frontend.c | 3 ++- 11 files changed, 100 insertions(+), 18 deletions(-) -- 2.22.0.410.gd8fdbe21b5-goog