Brian Mak <makb@xxxxxxxxxxx> writes: > Large cores may be truncated in some scenarios, such as with daemons > with stop timeouts that are not large enough or lack of disk space. This > impacts debuggability with large core dumps since critical information > necessary to form a usable backtrace, such as stacks and shared library > information, are omitted. > > We attempted to figure out which VMAs are needed to create a useful > backtrace, and it turned out to be a non-trivial problem. Instead, we > try simply sorting the VMAs by size, which has the intended effect. > > By sorting VMAs by dump size and dumping in that order, we have a > simple, yet effective heuristic. To make finding the history easier I would include: v1: https://lkml.kernel.org/r/CB8195AE-518D-44C9-9841-B2694A5C4002@xxxxxxxxxxx v2: https://lkml.kernel.org/r/C21B229F-D1E6-4E44-B506-A5ED4019A9DE@xxxxxxxxxxx Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> As Kees has already picked this up this is quite possibly silly. But *shrug* that was when I was out. > Signed-off-by: Brian Mak <makb@xxxxxxxxxxx> > --- > > Hi all, > > Still need to run rr tests on this, per Kees Cook's suggestion, will > update back once done. GDB and readelf show that this patch works > without issue though. > > Thanks, > Brian Mak > > v3: Edited commit message to better convey alternative solution as > non-trivial > > Moved sorting logic to fs/coredump.c to make it in place > > Above edits suggested by Eric Biederman <ebiederm@xxxxxxxxxxxx> > > v2: Edited commit message to include more reasoning for sorting VMAs > > Removed conditional VMA sorting with debugfs knob > > Above edits suggested by Eric Biederman <ebiederm@xxxxxxxxxxxx> > > fs/coredump.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/fs/coredump.c b/fs/coredump.c > index 7f12ff6ad1d3..33c5ac53ab31 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -18,6 +18,7 @@ > #include <linux/personality.h> > #include <linux/binfmts.h> > #include <linux/coredump.h> > +#include <linux/sort.h> > #include <linux/sched/coredump.h> > #include <linux/sched/signal.h> > #include <linux/sched/task_stack.h> > @@ -1191,6 +1192,18 @@ static void free_vma_snapshot(struct coredump_params *cprm) > } > } > > +static int cmp_vma_size(const void *vma_meta_lhs_ptr, const void *vma_meta_rhs_ptr) > +{ > + const struct core_vma_metadata *vma_meta_lhs = vma_meta_lhs_ptr; > + const struct core_vma_metadata *vma_meta_rhs = vma_meta_rhs_ptr; > + > + if (vma_meta_lhs->dump_size < vma_meta_rhs->dump_size) > + return -1; > + if (vma_meta_lhs->dump_size > vma_meta_rhs->dump_size) > + return 1; > + return 0; > +} > + > /* > * Under the mmap_lock, take a snapshot of relevant information about the task's > * VMAs. > @@ -1253,5 +1266,8 @@ static bool dump_vma_snapshot(struct coredump_params *cprm) > cprm->vma_data_size += m->dump_size; > } > > + sort(cprm->vma_meta, cprm->vma_count, sizeof(*cprm->vma_meta), > + cmp_vma_size, NULL); > + > return true; > } > > base-commit: eb5e56d1491297e0881c95824e2050b7c205f0d4
