diff options
| author | Thomas Gleixner <tglx@linutronix.de> | 2021-07-29 13:01:59 +0200 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2021-08-28 01:33:02 +0200 |
| commit | b542e383d8c005f06a131e2b40d5889b812f19c6 (patch) | |
| tree | 14a6c55f5366f44df978f27c4b8a92f0a30b0689 /include | |
| parent | 366e7ad6ba5f4cb2ffd0b7316e404d6ee9c0f401 (diff) | |
eventfd: Make signal recursion protection a task bit
The recursion protection for eventfd_signal() is based on a per CPU
variable and relies on the !RT semantics of spin_lock_irqsave() for
protecting this per CPU variable. On RT kernels spin_lock_irqsave() neither
disables preemption nor interrupts which allows the spin lock held section
to be preempted. If the preempting task invokes eventfd_signal() as well,
then the recursion warning triggers.
Paolo suggested to protect the per CPU variable with a local lock, but
that's heavyweight and actually not necessary. The goal of this protection
is to prevent the task stack from overflowing, which can be achieved with a
per task recursion protection as well.
Replace the per CPU variable with a per task bit similar to other recursion
protection bits like task_struct::in_page_owner. This works on both !RT and
RT kernels and removes as a side effect the extra per CPU storage.
No functional change for !RT kernels.
Reported-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/87wnp9idso.ffs@tglx
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/eventfd.h | 11 | ||||
| -rw-r--r-- | include/linux/sched.h | 4 |
2 files changed, 9 insertions, 6 deletions
diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index fa0a524baed0..305d5f19093b 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -14,6 +14,7 @@ #include <linux/err.h> #include <linux/percpu-defs.h> #include <linux/percpu.h> +#include <linux/sched.h> /* * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining @@ -43,11 +44,9 @@ int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *w __u64 *cnt); void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt); -DECLARE_PER_CPU(int, eventfd_wake_count); - -static inline bool eventfd_signal_count(void) +static inline bool eventfd_signal_allowed(void) { - return this_cpu_read(eventfd_wake_count); + return !current->in_eventfd_signal; } #else /* CONFIG_EVENTFD */ @@ -78,9 +77,9 @@ static inline int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, return -ENOSYS; } -static inline bool eventfd_signal_count(void) +static inline bool eventfd_signal_allowed(void) { - return false; + return true; } static inline void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt) diff --git a/include/linux/sched.h b/include/linux/sched.h index 3bb9fecfdaa1..6421a9a8b4ca 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -864,6 +864,10 @@ struct task_struct { /* Used by page_owner=on to detect recursion in page tracking. */ unsigned in_page_owner:1; #endif +#ifdef CONFIG_EVENTFD + /* Recursion prevention for eventfd_signal() */ + unsigned in_eventfd_signal:1; +#endif unsigned long atomic_flags; /* Flags requiring atomic access. */ |