14:10 <irker745> systemtap: sapatel systemtap.git:probewrite * release-4.3-52-gc64427412 / man/stap.1.in man/stapprobes.3stap man/stapref.1: Add docs for @probewrite.

17:23 <agentzh> fche: does this patch make sense at all? https://gist.github.com/agentzh/7a9095fe5f720a155b3e6eabe6a3fab3

17:23 <agentzh> some intel engineers suggested to us that we should acquire the mm sem when accessing the target memory.

17:24 <fche> is there a test case for this?\

17:24 <fche> something showing a problem with the status quo?

17:25 <agentzh> no test cases, just in the light of potential race conditions.

17:25 <agentzh> just asking for opinions.

17:26 <agentzh> not meant to be merged into the master atm.

17:27 <fche> does the kernel take the mm_sem in routine userspace access functions?

17:27 <fche> like when copying out syscall parameters or whatever?

17:27 <fche> I thought it was taken generally around *changes* to the memory map

17:33 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-45-g38b8e50fd / tapset/registers.stp tapset/x86_64/registers.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Add functions for writing to syscall args and testcase.

17:33 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-46-gf33960c71 / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Fix sysarg write testcase

17:33 <irker562> systemtap: sapatel systemtap.git:probewrite_new * release-4.3-48-g9a6116de7 / NEWS elaborate.cxx elaborate.h parse.cxx staptree.cxx staptree.h testsuite/systemtap.base/probewrite.exp testsuite/systemtap.base/probewrite_1.stp testsuite/systemtap.base/probewrite_2.stp testsuite/systemtap.base/probewrite_3.c testsuite/systemtap.base/probewrite_3.stp translate.cxx: PR26015: Add @probewrite predicate.

17:33 <irker562> systemtap: sapatel systemtap.git:probewrite_new * release-4.3-49-gd0d42395e / man/stap.1.in man/stapprobes.3stap man/stapref.1: Add docs for @probewrite.

17:33 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-47-gcd3dc694d / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp: Add string modification to syscall arg write test

17:34 <agentzh> fche: my hunch is that if stap can make sure no other things would ever change mm when its probe handlers are running, then it should be fine.

17:35 <agentzh> for process_vm_readv() syscall, it does acquire the mm sem when reading the remote memory. but for them, it might make more sense since the target is not stopped anyway.

17:36 <agentzh> i.e., here: https://github.com/torvalds/linux/blob/master/mm/process_vm_access.c#L107

17:38 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-45-g38b8e50fd / tapset/registers.stp tapset/x86_64/registers.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Add functions for writing to syscall args and testcase.

17:38 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-46-gf33960c71 / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Fix sysarg write testcase

17:38 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-47-gcd3dc694d / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp: Add string modification to syscall arg write test

17:38 <irker562> systemtap: sapatel systemtap.git:probewrite_new * release-4.3-48-g9a6116de7 / NEWS elaborate.cxx elaborate.h parse.cxx staptree.cxx staptree.h testsuite/systemtap.base/probewrite.exp testsuite/systemtap.base/probewrite_1.stp testsuite/systemtap.base/probewrite_2.stp testsuite/systemtap.base/probewrite_3.c testsuite/systemtap.base/probewrite_3.stp translate.cxx: PR26015: Add @probewrite predicate.

17:38 <irker562> systemtap: sapatel systemtap.git:probewrite_new * release-4.3-49-gd0d42395e / man/stap.1.in man/stapprobes.3stap man/stapref.1: Add docs for @probewrite.

17:42 <irker562> systemtap: sapatel systemtap.git:probewrite_new * release-4.3-45-gf30345c96 / NEWS elaborate.cxx elaborate.h parse.cxx staptree.cxx staptree.h testsuite/systemtap.base/probewrite.exp testsuite/systemtap.base/probewrite_1.stp testsuite/systemtap.base/probewrite_2.stp testsuite/systemtap.base/probewrite_3.c testsuite/systemtap.base/probewrite_3.stp translate.cxx: PR26015: Add @probewrite predicate.

17:42 <irker562> systemtap: sapatel systemtap.git:probewrite_new * release-4.3-46-g038cd8a3f / man/stap.1.in man/stapprobes.3stap man/stapref.1: Add docs for @probewrite.

17:42 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-47-gc2573f362 / tapset/registers.stp tapset/x86_64/registers.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Add functions for writing to syscall args and testcase.

17:42 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-48-g72bd18afe / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Fix sysarg write testcase

17:42 <irker562> systemtap: amerey systemtap.git:probewrite_new * release-4.3-49-g50b7a1a7c / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp: Add string modification to syscall arg write test

17:45 <irker562> systemtap: sapatel systemtap.git:PR26015 * release-4.3-45-gf30345c96 / NEWS elaborate.cxx elaborate.h parse.cxx staptree.cxx staptree.h testsuite/systemtap.base/probewrite.exp testsuite/systemtap.base/probewrite_1.stp testsuite/systemtap.base/probewrite_2.stp testsuite/systemtap.base/probewrite_3.c testsuite/systemtap.base/probewrite_3.stp translate.cxx: PR26015: Add @probewrite predicate.

17:45 <irker562> systemtap: sapatel systemtap.git:PR26015 * release-4.3-46-g038cd8a3f / man/stap.1.in man/stapprobes.3stap man/stapref.1: Add docs for @probewrite.

17:45 <irker562> systemtap: amerey systemtap.git:PR26015 * release-4.3-47-gc2573f362 / tapset/registers.stp tapset/x86_64/registers.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Add functions for writing to syscall args and testcase.

17:45 <irker562> systemtap: amerey systemtap.git:PR26015 * release-4.3-48-g72bd18afe / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp testsuite/systemtap.syscall/mkdir_probewrite.exp testsuite/systemtap.syscall/mkdir_probewrite.stp: Fix sysarg write testcase

17:45 <irker562> systemtap: amerey systemtap.git:PR26015 * release-4.3-49-g50b7a1a7c / testsuite/systemtap.base/sysarg_write.c testsuite/systemtap.base/sysarg_write.exp testsuite/systemtap.base/sysarg_write.stp: Add string modification to syscall arg write test

17:50 <fche> agentzh, process_vm_readv I believe applies across processes, whereas stap user-space fetches apply to the current process only

19:05 <irker562> systemtap: fche systemtap.git:master * release-4.3-64-g25012d82e / NEWS man/stap.1.in runtime/common_probe_context.h staptree.h tapsets.cxx testsuite/systemtap.base/lock-pushdown.exp testsuite/systemtap.base/lock-pushdown.stp translate.cxx: PR26296: lock pushdown optimization

19:48 <agentzh> fche: yeah, that's a difference.