user/sven/linux.git/include/linux/srcu.h, branch v6.14.8

Merge branches 'fixes.2024.12.14a', 'rcutorture.2024.12.14a', 'srcu.2024.12.14a' and 'torture-test.2024.12.14a' into rcu-merge.2024.12.14a

2024-12-14T16:32:26Z

fixes.2024.12.14a: RCU fixes rcutorture.2024.12.14a: Torture-test updates srcu.2024.12.14a: SRCU updates torture-test.2024.12.14a: Adding an extra test, fixes

srcu: Guarantee non-negative return value from srcu_read_lock()

2024-12-14T16:13:09Z

For almost 20 years, the int return value from srcu_read_lock() has been always either zero or one. This commit therefore documents the fact that it will be non-negative, and does the same for the underlying __srcu_read_lock(). [ paulmck: Apply Andrii Nakryiko feedback. ] Signed-off-by: Paul E. McKenney Acked-by: Andrii Nakryiko Acked-by: Peter Zijlstra (Intel) Signed-off-by: Uladzislau Rezki (Sony)

rcutorture: Use symbols for SRCU reader flavors

2024-12-14T16:06:08Z

This commit converts rcutorture.c values for the reader_flavor module parameter from hexadecimal to the SRCU_READ_FLAVOR_* C-preprocessor macros. The actual modprobe or kernel-boot-parameter values for read_flavor must still be entered in hexadecimal. Link: https://lore.kernel.org/all/c48c9dca-fe07-4833-acaa-28c827e5a79e@amd.com/ Suggested-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney Signed-off-by: Uladzislau Rezki (Sony)

srcu: Unconditionally record srcu_read_lock_lite() in ->srcu_reader_flavor

2024-11-15T21:13:37Z

Currently, srcu_read_lock_lite() uses the SRCU_READ_FLAVOR_LITE bit in ->srcu_reader_flavor to communicate to the grace-period processing in srcu_readers_active_idx_check() that the smp_mb() must be replaced by a synchronize_rcu(). Unfortunately, ->srcu_reader_flavor is not updated unless the kernel is built with CONFIG_PROVE_RCU=y. Therefore in all kernels built with CONFIG_PROVE_RCU=n, srcu_readers_active_idx_check() incorrectly uses smp_mb() instead of synchronize_rcu() for srcu_struct structures whose readers use srcu_read_lock_lite(). This commit therefore causes Tree SRCU srcu_read_lock_lite() to unconditionally update ->srcu_reader_flavor so that srcu_readers_active_idx_check() can make the correct choice. Reported-by: Neeraj Upadhyay Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/ Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()") Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker

srcu: Remove smp_mb() from srcu_read_unlock_lite()

2024-11-12T22:30:33Z

The srcu_read_unlock_lite() function invokes __srcu_read_unlock() instead of __srcu_read_unlock_lite(), which means that it is doing an unnecessary smp_mb(). This is harmless other than the performance degradation. This commit therefore switches to __srcu_read_unlock_lite(). Reported-by: Neeraj Upadhyay Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/ Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()") Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker

srcu: Improve srcu_read_lock_lite() kernel-doc comment

2024-11-12T14:45:12Z

Where RCU is watching is where it is OK to invoke rcu_read_lock(). Reported-by: Andrii Nakryiko Signed-off-by: Paul E. McKenney Acked-by: Andrii Nakryiko Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker

srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()

2024-11-12T14:43:34Z

This patch adds srcu_read_lock_lite() and srcu_read_unlock_lite(), which dispense with the read-side smp_mb() but also are restricted to code regions that RCU is watching. If a given srcu_struct structure uses srcu_read_lock_lite() and srcu_read_unlock_lite(), it is not permitted to use any other SRCU read-side marker, before, during, or after. Another price of light-weight readers is heavier weight grace periods. Such readers mean that SRCU grace periods on srcu_struct structures used by light-weight readers will incur at least two calls to synchronize_rcu(). In addition, normal SRCU grace periods for light-weight-reader srcu_struct structures never auto-expedite. Note that expedited SRCU grace periods for light-weight-reader srcu_struct structures still invoke synchronize_rcu(), not synchronize_srcu_expedited(). Something about wishing to keep the IPIs down to a dull roar. The srcu_read_lock_lite() and srcu_read_unlock_lite() functions may not (repeat, *not*) be used from NMI handlers, but if this is needed, an additional flavor of SRCU reader can be added by some future commit. [ paulmck: Apply Alexei Starovoitov expediting feedback. ] [ paulmck: Apply kernel test robot feedback. ] Signed-off-by: Paul E. McKenney Tested-by: kernel test robot Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: Peter Zijlstra Cc: Kent Overstreet Cc: Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker

srcu: Create CPP macros for normal and NMI-safe SRCU readers

2024-11-12T14:43:21Z

This commit creates SRCU_READ_FLAVOR_NORMAL and SRCU_READ_FLAVOR_NMI C-preprocessor macros for srcu_read_lock() and srcu_read_lock_nmisafe(), respectively. These replace the old true/false values that were previously passed to srcu_check_read_flavor(). In addition, the srcu_check_read_flavor() function itself requires a bit of rework to handle bitmasks instead of true/false values. Signed-off-by: Paul E. McKenney Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: Peter Zijlstra Cc: Kent Overstreet Cc: Signed-off-by: Paul E. McKenney Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker

srcu: Improve srcu_read_lock{,_nmisafe}() comments

2024-11-12T14:43:06Z

This commit adds some additional usage constraints to the kernel-doc headers of srcu_read_lock() and srcu_read_lock_nmi_safe(). Suggested-by: Andrii Nakryiko Signed-off-by: Paul E. McKenney Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker

srcu: Renaming in preparation for additional reader flavor

2024-11-12T14:41:30Z

Currently, there are only two flavors of readers, normal and NMI-safe. A number of fields, functions, and types reflect this restriction. This renaming-only commit prepares for the addition of light-weight (as in memory-barrier-free) readers. OK, OK, there is also a drive-by white-space fixeup! Signed-off-by: Paul E. McKenney Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: Peter Zijlstra Cc: Kent Overstreet Cc: Reviewed-by: Neeraj Upadhyay Signed-off-by: Frederic Weisbecker