leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

bpf: Introduce helper bpf_find_vma

Browse Source 
In some profiler use cases, it is necessary to map an address to the
backing file, e.g., a shared library. bpf_find_vma helper provides a
flexible way to achieve this. bpf_find_vma maps an address of a task to
the vma (vm_area_struct) for this address, and feed the vma to an callback
BPF function. The callback function is necessary here, as we need to
ensure mmap_sem is unlocked.

It is necessary to lock mmap_sem for find_vma. To lock and unlock mmap_sem
safely when irqs are disable, we use the same mechanism as stackmap with
build_id. Specifically, when irqs are disabled, the unlocked is postponed
in an irq_work. Refactor stackmap.c so that the irq_work is shared among
bpf_find_vma and stackmap helpers.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Hengqi Chen <hengqi.chen@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211105232330.1936330-2-songliubraving@fb.com
This commit is contained in:
Song Liu
2021-11-05 16:23:29 -07:00
committed by Alexei Starovoitov
parent 5fd79ed9be
commit 7c7e3d31e7
9 changed files with 222 additions and 81 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
tools/include/uapi/linux/bpf.h
View File

@@ -4938,6 +4938,25 @@ union bpf_attr {
* **-ENOENT** if symbol is not found.
*
* **-EPERM** if caller does not have permission to obtain kernel address.
*
* long bpf_find_vma(struct task_struct *task, u64 addr, void *callback_fn, void *callback_ctx, u64 flags)
* Description
* Find vma of *task* that contains *addr*, call *callback_fn*
* function with *task*, *vma*, and *callback_ctx*.
* The *callback_fn* should be a static function and
* the *callback_ctx* should be a pointer to the stack.
* The *flags* is used to control certain aspects of the helper.
* Currently, the *flags* must be 0.
*
* The expected callback signature is
*
* long (\*callback_fn)(struct task_struct \*task, struct vm_area_struct \*vma, void \*callback_ctx);
*
* Return
* 0 on success.
* **-ENOENT** if *task->mm* is NULL, or no vma contains *addr*.
* **-EBUSY** if failed to try lock mmap_lock.
* **-EINVAL** for invalid **flags**.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -5120,6 +5139,7 @@ union bpf_attr {
FN(trace_vprintk), \
FN(skc_to_unix_sock), \
FN(kallsyms_lookup_name), \
FN(find_vma), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper