While running a user_access regions, it is not supported to reschedule. Add an overridable primitive to indicate whether a user_access region is active and check that this is not the case when calling rescheduling functions.
These checks are only performed when DEBUG_UACCESS_SLEEP is selected. Also, add a comment clarifying the behaviour of user_access regions. Signed-off-by: Julien Thierry <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> --- include/linux/kernel.h | 11 +++++++++-- include/linux/uaccess.h | 13 +++++++++++++ kernel/sched/core.c | 22 ++++++++++++++++++++++ lib/Kconfig.debug | 8 ++++++++ 4 files changed, 52 insertions(+), 2 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 8f0e68e..73f1f82 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -237,11 +237,18 @@ struct pt_regs; struct user; +#ifdef CONFIG_DEBUG_UACCESS_SLEEP +extern void __might_resched(const char *file, int line); +#else +#define __might_resched(file, line) do { } while (0) +#endif + #ifdef CONFIG_PREEMPT_VOLUNTARY extern int _cond_resched(void); -# define might_resched() _cond_resched() +# define might_resched() \ + do { __might_resched(__FILE__, __LINE__); _cond_resched(); } while (0) #else -# define might_resched() do { } while (0) +# define might_resched() __might_resched(__FILE__, __LINE__) #endif #ifdef CONFIG_DEBUG_ATOMIC_SLEEP diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 37b226e..2c0c39e 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -263,6 +263,15 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, #define probe_kernel_address(addr, retval) \ probe_kernel_read(&retval, addr, sizeof(retval)) +/* + * user_access_begin() and user_access_end() define a region where + * unsafe user accessors can be used. Exceptions and interrupt shall exit the + * user_access region and re-enter it when returning to the interrupted context. + * + * No sleeping function should get called during a user_access region - we rely + * on exception handling to take care of the user_access status for us, but that + * doesn't happen when directly calling schedule(). + */ #ifndef user_access_begin #define user_access_begin(ptr,len) access_ok(ptr, len) #define user_access_end() do { } while (0) @@ -270,6 +279,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to, #define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0) #endif +#ifndef unsafe_user_region_active +#define unsafe_user_region_active() false +#endif + #ifdef CONFIG_HARDENED_USERCOPY void usercopy_warn(const char *name, const char *detail, bool to_user, unsigned long offset, unsigned long len); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a674c7db..b1bb7e9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3289,6 +3289,14 @@ static inline void schedule_debug(struct task_struct *prev) __schedule_bug(prev); preempt_count_set(PREEMPT_DISABLED); } + + if (IS_ENABLED(CONFIG_DEBUG_UACCESS_SLEEP) && + unlikely(unsafe_user_region_active())) { + printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n", + prev->comm, prev->pid, preempt_count()); + dump_stack(); + } + rcu_sleep_check(); profile_hit(SCHED_PROFILING, __builtin_return_address(0)); @@ -6151,6 +6159,20 @@ void ___might_sleep(const char *file, int line, int preempt_offset) EXPORT_SYMBOL(___might_sleep); #endif +#ifdef CONFIG_DEBUG_UACCESS_SLEEP +void __might_resched(const char *file, int line) +{ + if (!unsafe_user_region_active()) + return; + + printk(KERN_ERR + "BUG: rescheduling function called from user access context at %s:%d\n", + file, line); + dump_stack(); +} +EXPORT_SYMBOL(__might_resched); +#endif + #ifdef CONFIG_MAGIC_SYSRQ void normalize_rt_tasks(void) { diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index d4df5b2..d030e31 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2069,6 +2069,14 @@ config IO_STRICT_DEVMEM If in doubt, say Y. +config DEBUG_UACCESS_SLEEP + bool "Check sleep inside a user access region" + depends on DEBUG_KERNEL + help + If you say Y here, various routines which may sleep will become very + noisy if they are called inside a user access region (i.e. between + a user_access_begin() and a user_access_end()) + source "arch/$(SRCARCH)/Kconfig.debug" endmenu # Kernel hacking -- 1.9.1
