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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-07-31 09:21:13 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-07-31 09:21:13 -0700 |
| commit | 5e4823e6dab8fcc897757c1be68d157a369e4bb5 (patch) | |
| tree | 6958c902b6b0754d14d54ccb0cca1f38cfa83072 /kernel | |
| parent | cd2715b7929bcaf6e38d13ac512e0a9bba8df10d (diff) | |
| parent | 6eebd5fb20838f5971ba17df9f55cc4f84a31053 (diff) | |
| download | linux-5e4823e6dab8fcc897757c1be68d157a369e4bb5.tar.gz | |
Merge tag 'locking_urgent_for_v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fix from Borislav Petkov: - Avoid rwsem lockups in certain situations when handling the handoff bit * tag 'locking_urgent_for_v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: locking/rwsem: Allow slowpath writer to ignore handoff bit if not set by first waiter
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/rwsem.c | 30 |
1 files changed, 20 insertions, 10 deletions
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c index 9d1db4a54d34..65f0262f635e 100644 --- a/kernel/locking/rwsem.c +++ b/kernel/locking/rwsem.c @@ -335,8 +335,6 @@ struct rwsem_waiter { struct task_struct *task; enum rwsem_waiter_type type; unsigned long timeout; - - /* Writer only, not initialized in reader */ bool handoff_set; }; #define rwsem_first_waiter(sem) \ @@ -459,10 +457,12 @@ static void rwsem_mark_wake(struct rw_semaphore *sem, * to give up the lock), request a HANDOFF to * force the issue. */ - if (!(oldcount & RWSEM_FLAG_HANDOFF) && - time_after(jiffies, waiter->timeout)) { - adjustment -= RWSEM_FLAG_HANDOFF; - lockevent_inc(rwsem_rlock_handoff); + if (time_after(jiffies, waiter->timeout)) { + if (!(oldcount & RWSEM_FLAG_HANDOFF)) { + adjustment -= RWSEM_FLAG_HANDOFF; + lockevent_inc(rwsem_rlock_handoff); + } + waiter->handoff_set = true; } atomic_long_add(-adjustment, &sem->count); @@ -599,7 +599,7 @@ rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter, static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, struct rwsem_waiter *waiter) { - bool first = rwsem_first_waiter(sem) == waiter; + struct rwsem_waiter *first = rwsem_first_waiter(sem); long count, new; lockdep_assert_held(&sem->wait_lock); @@ -609,11 +609,20 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF); if (has_handoff) { - if (!first) + /* + * Honor handoff bit and yield only when the first + * waiter is the one that set it. Otherwisee, we + * still try to acquire the rwsem. + */ + if (first->handoff_set && (waiter != first)) return false; - /* First waiter inherits a previously set handoff bit */ - waiter->handoff_set = true; + /* + * First waiter can inherit a previously set handoff + * bit and spin on rwsem if lock acquisition fails. + */ + if (waiter == first) + waiter->handoff_set = true; } new = count; @@ -1027,6 +1036,7 @@ queue: waiter.task = current; waiter.type = RWSEM_WAITING_FOR_READ; waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT; + waiter.handoff_set = false; raw_spin_lock_irq(&sem->wait_lock); if (list_empty(&sem->wait_list)) { |