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a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=meVymXHHAAAA:8 a=BlFbigHyMx7Wt0vz_rsA:9 a=QEXdDO2ut3YA:10 a=2JgSa4NbpEOStq-L5dxp:22 cc=ntf awl=host:13604 X-Proofpoint-GUID: GLsH1vOptIBoOM9RgaCUVSuckgAtFiQ- X-Proofpoint-ORIG-GUID: GLsH1vOptIBoOM9RgaCUVSuckgAtFiQ- X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzMwMDAzMiBTYWx0ZWRfX87gyoq0IZoZl uwcH3ezhBhNZeXTKnCGUdIZdlx3s+ZH/op+/SgMB2BffnHqAC8ohRHYwPx26yXmrvE/7QOqZdm+ 0vKg76W35Lx4GOwfke+lTBhDBqB3udv8aseD081xxmA0SFPBTWudwDQzuAbNHvLxPuDGO/6WSjh KD2a9U4hppFBZreT5rEJDh5Jc8ocTyj+b+PzZCy2h5ypqtjZ5Wk1XfdJ64Gw/eCCXhTSeYwx5VN 9aJc/E/6ExEqHZl1+0nkVYdqPUtrLAcQW8w8unlrxWFm8k1PrMiGGES7Mw0qhYsD/n7zSCLsZnP mxaaYqNaL10C7DRCfsUbRNGaW2V1ADcn++LgFVwD9MbSMoTcXTIryg2FeF/2hpogQLybNeTXX7Z CdTr64dOJUVA9s9j4s3dKYQxJ+e1afcN39rRkrXAfs+axtPxg/RotVCPPNeWxewYR+2QkO9R On 7/29/25 11:23 AM, Steven Rostedt wrote: > From: Josh Poimboeuf > > Cache the results of the unwind to ensure the unwind is only performed > once, even when called by multiple tracers. > > The cache nr_entries gets cleared every time the task exits the kernel. > When a stacktrace is requested, nr_entries gets set to the number of > entries in the stacktrace. If another stacktrace is requested, if > nr_entries is not zero, then it contains the same stacktrace that would be > retrieved so it is not processed again and the entries is given to the > caller. > > Reviewed-by: Jens Remus > Co-developed-by: Steven Rostedt (Google) > Signed-off-by: Josh Poimboeuf > Signed-off-by: Steven Rostedt (Google) > Signed-off-by: Steven Rostedt (Google) > --- > include/linux/entry-common.h | 2 ++ > include/linux/unwind_deferred.h | 8 +++++++ > include/linux/unwind_deferred_types.h | 7 +++++- > kernel/unwind/deferred.c | 31 +++++++++++++++++++++------ > 4 files changed, 40 insertions(+), 8 deletions(-) > > diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h > index f94f3fdf15fc..8908b8eeb99b 100644 > --- a/include/linux/entry-common.h > +++ b/include/linux/entry-common.h > @@ -12,6 +12,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -362,6 +363,7 @@ static __always_inline void exit_to_user_mode(void) > lockdep_hardirqs_on_prepare(); > instrumentation_end(); > > + unwind_reset_info(); > user_enter_irqoff(); > arch_exit_to_user_mode(); > lockdep_hardirqs_on(CALLER_ADDR0); > diff --git a/include/linux/unwind_deferred.h b/include/linux/unwind_deferred.h > index a5f6e8f8a1a2..baacf4a1eb4c 100644 > --- a/include/linux/unwind_deferred.h > +++ b/include/linux/unwind_deferred.h > @@ -12,6 +12,12 @@ void unwind_task_free(struct task_struct *task); > > int unwind_user_faultable(struct unwind_stacktrace *trace); > > +static __always_inline void unwind_reset_info(void) > +{ > + if (unlikely(current->unwind_info.cache)) > + current->unwind_info.cache->nr_entries = 0; > +} Should the entries[] items upto nr_entries (stack trace info from the previous request) also be reset to 0 here ? > + > #else /* !CONFIG_UNWIND_USER */ > > static inline void unwind_task_init(struct task_struct *task) {} > @@ -19,6 +25,8 @@ static inline void unwind_task_free(struct task_struct *task) {} > > static inline int unwind_user_faultable(struct unwind_stacktrace *trace) { return -ENOSYS; } > > +static inline void unwind_reset_info(void) {} > + > #endif /* !CONFIG_UNWIND_USER */ > > #endif /* _LINUX_UNWIND_USER_DEFERRED_H */ > diff --git a/include/linux/unwind_deferred_types.h b/include/linux/unwind_deferred_types.h > index aa32db574e43..db5b54b18828 100644 > --- a/include/linux/unwind_deferred_types.h > +++ b/include/linux/unwind_deferred_types.h > @@ -2,8 +2,13 @@ > #ifndef _LINUX_UNWIND_USER_DEFERRED_TYPES_H > #define _LINUX_UNWIND_USER_DEFERRED_TYPES_H > > +struct unwind_cache { > + unsigned int nr_entries; > + unsigned long entries[]; > +}; > + Should we use __counted_by ? > struct unwind_task_info { > - unsigned long *entries; > + struct unwind_cache *cache; > }; > > #endif /* _LINUX_UNWIND_USER_DEFERRED_TYPES_H */ > diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c > index a0badbeb3cc1..96368a5aa522 100644 > --- a/kernel/unwind/deferred.c > +++ b/kernel/unwind/deferred.c > @@ -4,10 +4,13 @@ > */ > #include > #include > +#include > #include > #include > > -#define UNWIND_MAX_ENTRIES 512 > +/* Make the cache fit in a 4K page */ > +#define UNWIND_MAX_ENTRIES \ > + ((SZ_4K - sizeof(struct unwind_cache)) / sizeof(long)) > > /** > * unwind_user_faultable - Produce a user stacktrace in faultable context > @@ -24,6 +27,7 @@ > int unwind_user_faultable(struct unwind_stacktrace *trace) > { > struct unwind_task_info *info = ¤t->unwind_info; > + struct unwind_cache *cache; > > /* Should always be called from faultable context */ > might_fault(); > @@ -31,17 +35,30 @@ int unwind_user_faultable(struct unwind_stacktrace *trace) > if (current->flags & PF_EXITING) > return -EINVAL; > > - if (!info->entries) { > - info->entries = kmalloc_array(UNWIND_MAX_ENTRIES, sizeof(long), > - GFP_KERNEL); > - if (!info->entries) > + if (!info->cache) { > + info->cache = kzalloc(struct_size(cache, entries, UNWIND_MAX_ENTRIES), > + GFP_KERNEL); > + if (!info->cache) > return -ENOMEM; > } > > + cache = info->cache; > + trace->entries = cache->entries; > + > + if (cache->nr_entries) { > + /* > + * The user stack has already been previously unwound in this > + * entry context. Skip the unwind and use the cache. > + */ > + trace->nr = cache->nr_entries; > + return 0; > + } > + > trace->nr = 0; > - trace->entries = info->entries; > unwind_user(trace, UNWIND_MAX_ENTRIES); > > + cache->nr_entries = trace->nr; > + > return 0; > } > > @@ -56,5 +73,5 @@ void unwind_task_free(struct task_struct *task) > { > struct unwind_task_info *info = &task->unwind_info; > > - kfree(info->entries); > + kfree(info->cache); > }