On Wed, Sep 10, 2025 at 2:10 AM Saket Kumar Bhaskar <skb99@xxxxxxxxxxxxx> wrote:
>
> On Tue, Jul 30, 2024 at 01:03:17PM -0700, Andrii Nakryiko wrote:
> > On Sun, Jul 28, 2024 at 12:38 PM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
> > >
> > > On Fri, Jul 26, 2024 at 05:37:55PM -0700, Andrii Nakryiko wrote:
> > > > On Fri, Jul 26, 2024 at 5:27 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
> > > > >
> > > > > On Thu, Jul 25, 2024 at 01:03:55PM -0700, Andrii Nakryiko wrote:
> > > > > > On Thu, Jul 25, 2024 at 5:12 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Wed, Jul 24, 2024 at 03:52:10PM -0700, Andrii Nakryiko wrote:
> > > > > > > > Add a new set of tests validating behavior of capturing stack traces
> > > > > > > > with build ID. We extend uprobe_multi target binary with ability to
> > > > > > > > trigger uprobe (so that we can capture stack traces from it), but also
> > > > > > > > we allow to force build ID data to be either resident or non-resident in
> > > > > > > > memory (see also a comment about quirks of MADV_PAGEOUT).
> > > > > > > >
> > > > > > > > That way we can validate that in non-sleepable context we won't get
> > > > > > > > build ID (as expected), but with sleepable uprobes we will get that
> > > > > > > > build ID regardless of it being physically present in memory.
> > > > > > > >
> > > > > > > > Also, we add a small add-on linker script which reorders
> > > > > > > > .note.gnu.build-id section and puts it after (big) .text section,
> > > > > > > > putting build ID data outside of the very first page of ELF file. This
> > > > > > > > will test all the relaxations we did in build ID parsing logic in kernel
> > > > > > > > thanks to freader abstraction.
> > > > > > > >
> > > > > > > > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > > > > > >
> > > > > > > one of my bpf selftests runs showed:
> > > > > > >
> > > > > > > test_build_id:PASS:parse_build_id 0 nsec
> > > > > > > subtest_nofault:PASS:skel_open 0 nsec
> > > > > > > subtest_nofault:PASS:link 0 nsec
> > > > > > > subtest_nofault:PASS:trigger_uprobe 0 nsec
> > > > > > > subtest_nofault:PASS:res 0 nsec
> > > > > > > subtest_nofault:FAIL:build_id_status unexpected build_id_status: actual 1 != expected 2
> > > > > > > #42/1 build_id/nofault-paged-out:FAIL
> > > > > > > #42/2 build_id/nofault-paged-in:OK
> > > > > > > #42/3 build_id/sleepable:OK
> > > > > > > #42 build_id:FAIL
> > > > > > >
> > > > > > > I could never reproduce again.. but I wonder the the page could sneak
> > > > > > > in before the bpf program is hit and the buildid will get parsed?
> > > > > > >
> > > > > >
> > > > > > Yes, and I just realized that I forgot to mark this test as serial. If
> > > > > > there is parallel test that also runs uprobe_multi and that causes
> > > > > > build_id page to be paged in into page cache, then this might succeed.
> > > > > > So I need to mark the test itself serial.
> > > > > >
> > > > > > Another issue which I was debugging (and fixed) yesterday was that if
> > > > > > the memory passed for MADV_PAGEOUT is not yet memory mapped into the
> > > > > > current process, then it won't be really removed from the page cache.
> > > > > > I avoid that by first paging it in, and then MADV_PAGEOUT.
> > > > >
> > > > > ok, I triggered that in serial run, so I probably hit this one
> > > > >
> > > >
> > > > you did it with v2 of the patch set? I had this bug in v1, but v2
> > > > should be fine, as far as I understand (due to unconditional
> > > > madvise(addr, page_sz, MADV_POPULATE_READ); before madvise(addr,
> > > > page_sz, MADV_PAGEOUT)). At least I haven't been able to reproduce
> > > > that anymore and BPF CI is now happy as well.
> > >
> > > yes, it's with v2 and I can still see that.. but only for the first run of
> > > the test after reboot.. so far I have no clue.. I can see the successful
> > > page-out madvise (still not sure how much is that telling about the page
> > > being paged out), and then the build id code sees the page just fine
> > >
> > > attaching my .config in case
> > >
> >
> > I wasn't able to repro this, sorry. It works very reliably for me with
> > your or my config. Given it also seems to work reliably in BPF CI, I'm
> > still inclined to add this tests, I think it's good to have that
> > coverage.
> >
> > I'll monitor, and if it becomes flaky, we'll need to reassess this, of course.
> >
> Hi Andrii and Jirka,
>
> I encountered this error on powerpc, which is happening quiet consistently:
>
> # ./test_progs -t build_id/nofault-paged-out
> serial_test_build_id:PASS:parse_build_id 0 nsec
> subtest_nofault:PASS:skel_open 0 nsec
> subtest_nofault:PASS:link 0 nsec
> subtest_nofault:PASS:trigger_uprobe 0 nsec
> subtest_nofault:PASS:res 0 nsec
> subtest_nofault:FAIL:build_id_status unexpected build_id_status: actual 1 != expected 2
> #46/1 build_id/nofault-paged-out:FAIL
> #46 build_id:FAIL
> #397 stacktrace_build_id:OK
> #398 stacktrace_build_id_nmi:OK
>
> I dumped vma mapping using pmap in trigger_uprobe function
> before/after MADV_POPULATE_READ and b/w MADV_POPULATE_READ
> and MADV_PAGEOUT, page residency using mincore() (as shown
> "Before uprobe: Page residency = ") and addr (as shown
> "Entered trigger_uprobe addr ->").
>
> Here I am putting out 3 scenarios:
>
> 1. #./test_progs -t build_id/nofault-paged-out
> Entered trigger_uprobe addr -> 0x105a0000
> 144992: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7744 704 64 r-x-- uprobe_multi
> 0000000010790000 64 64 64 r---- uprobe_multi
> 00000000107a0000 64 64 64 rw--- uprobe_multi
> 000001002bf90000 192 64 64 rw--- [ anon ]
> 00007fffb55d0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffb56a0000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffb56b0000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffb56c0000 2304 1280 0 r-x-- libc.so.6
> 00007fffb5900000 64 64 64 r---- libc.so.6
> 00007fffb5910000 64 64 64 rw--- libc.so.6
> 00007fffb5920000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffb5950000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffb5960000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffb5970000 192 64 0 r-x-- libelf-0.192.so
> 00007fffb59a0000 64 64 64 r---- libelf-0.192.so
> 00007fffb59b0000 64 0 0 rw--- [ anon ]
> 00007fffb59d0000 256 0 0 r---- [ anon ]
> 00007fffb5a10000 64 64 0 r-x-- [ anon ]
> 00007fffb5a20000 320 320 0 r-x-- ld64.so.2
> 00007fffb5a70000 64 64 64 r---- ld64.so.2
> 00007fffb5a80000 64 64 64 rw--- ld64.so.2
> 00007fffee7a0000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13056 3392 896
> 144992: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7744 704 64 r-x-- uprobe_multi
> 0000000010790000 64 64 64 r---- uprobe_multi
> 00000000107a0000 64 64 64 rw--- uprobe_multi
> 000001002bf90000 192 64 64 rw--- [ anon ]
> 00007fffb55d0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffb56a0000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffb56b0000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffb56c0000 2304 1344 0 r-x-- libc.so.6
> 00007fffb5900000 64 64 64 r---- libc.so.6
> 00007fffb5910000 64 64 64 rw--- libc.so.6
> 00007fffb5920000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffb5950000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffb5960000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffb5970000 192 64 0 r-x-- libelf-0.192.so
> 00007fffb59a0000 64 64 64 r---- libelf-0.192.so
> 00007fffb59b0000 64 0 0 rw--- [ anon ]
> 00007fffb59d0000 256 0 0 r---- [ anon ]
> 00007fffb5a10000 64 64 0 r-x-- [ anon ]
> 00007fffb5a20000 320 320 0 r-x-- ld64.so.2
> 00007fffb5a70000 64 64 64 r---- ld64.so.2
> 00007fffb5a80000 64 64 64 rw--- ld64.so.2
> 00007fffee7a0000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13056 3456 896
> 144992: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7744 704 64 r-x-- uprobe_multi
> 0000000010790000 64 64 64 r---- uprobe_multi
> 00000000107a0000 64 64 64 rw--- uprobe_multi
> 000001002bf90000 192 64 64 rw--- [ anon ]
> 00007fffb55d0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffb56a0000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffb56b0000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffb56c0000 2304 1344 0 r-x-- libc.so.6
> 00007fffb5900000 64 64 64 r---- libc.so.6
> 00007fffb5910000 64 64 64 rw--- libc.so.6
> 00007fffb5920000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffb5950000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffb5960000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffb5970000 192 64 0 r-x-- libelf-0.192.so
> 00007fffb59a0000 64 64 64 r---- libelf-0.192.so
> 00007fffb59b0000 64 0 0 rw--- [ anon ]
> 00007fffb59d0000 256 0 0 r---- [ anon ]
> 00007fffb5a10000 64 64 0 r-x-- [ anon ]
> 00007fffb5a20000 320 320 0 r-x-- ld64.so.2
> 00007fffb5a70000 64 64 64 r---- ld64.so.2
> 00007fffb5a80000 64 64 64 rw--- ld64.so.2
> 00007fffee7a0000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13056 3456 896
> Before uprobe: Page residency = resident
> After uprobe: Page residency = resident
> serial_test_build_id:PASS:parse_build_id 0 nsec
> subtest_nofault:PASS:skel_open 0 nsec
> subtest_nofault:PASS:link 0 nsec
> subtest_nofault:PASS:trigger_uprobe 0 nsec
> subtest_nofault:PASS:res 0 nsec
> subtest_nofault:FAIL:build_id_status unexpected build_id_status: actual 1 != expected 2
> #46/1 build_id/nofault-paged-out:FAIL
> #46 build_id:FAIL
> #397 stacktrace_build_id:OK
> #398 stacktrace_build_id_nmi:OK
>
> All error logs:
> serial_test_build_id:PASS:parse_build_id 0 nsec
> subtest_nofault:PASS:skel_open 0 nsec
> subtest_nofault:PASS:link 0 nsec
> subtest_nofault:PASS:trigger_uprobe 0 nsec
> subtest_nofault:PASS:res 0 nsec
> subtest_nofault:FAIL:build_id_status unexpected build_id_status: actual 1 != expected 2
> #46/1 build_id/nofault-paged-out:FAIL
> #46 build_id:FAIL
> Summary: 2/0 PASSED, 0 SKIPPED, 1 FAILED
>
> Here it can be seen that RSS for vma containing addr (0x105a0000)
> is not changing (remains 704) and the selftest fails.
>
> 2. When alignment in linker script is changed to 65536 (default
> page size in powerpc is 64k):
>
> git diff uprobe_multi.ld
> diff --git a/tools/testing/selftests/bpf/uprobe_multi.ld b/tools/testing/selftests/bpf/uprobe_multi.ld
> index a2e94828b..2063714b2 100644
> --- a/tools/testing/selftests/bpf/uprobe_multi.ld
> +++ b/tools/testing/selftests/bpf/uprobe_multi.ld
> @@ -1,8 +1,8 @@
> SECTIONS
> {
> - . = ALIGN(4096);
> + . = ALIGN(65536);
> .note.gnu.build-id : { *(.note.gnu.build-id) }
> - . = ALIGN(4096);
> + . = ALIGN(65536);
> }
> INSERT AFTER .text;
>
> #./test_progs -t build_id/nofault-paged-out -v
> bpf_testmod.ko is already unloaded.
> Loading bpf_testmod.ko...
> Successfully loaded bpf_testmod.ko.
> serial_test_build_id:PASS:parse_build_id 0 nsec
> subtest_nofault:PASS:skel_open 0 nsec
> subtest_nofault:PASS:link 0 nsec
> Entered trigger_uprobe addr -> 0x105b0000
> 145238: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7872 768 768 r-x-- uprobe_multi
> 00000000107b0000 64 64 64 r---- uprobe_multi
> 00000000107c0000 64 64 64 rw--- uprobe_multi
> 000001003a6b0000 192 64 64 rw--- [ anon ]
> 00007fffa3eb0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffa3f80000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffa3f90000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffa3fa0000 2304 1280 0 r-x-- libc.so.6
> 00007fffa41e0000 64 64 64 r---- libc.so.6
> 00007fffa41f0000 64 64 64 rw--- libc.so.6
> 00007fffa4200000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffa4230000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffa4240000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffa4250000 192 64 0 r-x-- libelf-0.192.so
> 00007fffa4280000 64 64 64 r---- libelf-0.192.so
> 00007fffa4290000 64 0 0 rw--- [ anon ]
> 00007fffa42b0000 256 0 0 r---- [ anon ]
> 00007fffa42f0000 64 64 0 r-x-- [ anon ]
> 00007fffa4300000 320 320 0 r-x-- ld64.so.2
> 00007fffa4350000 64 64 64 r---- ld64.so.2
> 00007fffa4360000 64 64 64 rw--- ld64.so.2
> 00007fffc6880000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13184 3456 1600
> 145238: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7872 832 832 r-x-- uprobe_multi
> 00000000107b0000 64 64 64 r---- uprobe_multi
> 00000000107c0000 64 64 64 rw--- uprobe_multi
> 000001003a6b0000 192 64 64 rw--- [ anon ]
> 00007fffa3eb0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffa3f80000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffa3f90000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffa3fa0000 2304 1344 0 r-x-- libc.so.6
> 00007fffa41e0000 64 64 64 r---- libc.so.6
> 00007fffa41f0000 64 64 64 rw--- libc.so.6
> 00007fffa4200000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffa4230000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffa4240000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffa4250000 192 64 0 r-x-- libelf-0.192.so
> 00007fffa4280000 64 64 64 r---- libelf-0.192.so
> 00007fffa4290000 64 0 0 rw--- [ anon ]
> 00007fffa42b0000 256 0 0 r---- [ anon ]
> 00007fffa42f0000 64 64 0 r-x-- [ anon ]
> 00007fffa4300000 320 320 0 r-x-- ld64.so.2
> 00007fffa4350000 64 64 64 r---- ld64.so.2
> 00007fffa4360000 64 64 64 rw--- ld64.so.2
> 00007fffc6880000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13184 3584 1664
> 145238: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7872 768 768 r-x-- uprobe_multi
> 00000000107b0000 64 64 64 r---- uprobe_multi
> 00000000107c0000 64 64 64 rw--- uprobe_multi
> 000001003a6b0000 192 64 64 rw--- [ anon ]
> 00007fffa3eb0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffa3f80000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffa3f90000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffa3fa0000 2304 1344 0 r-x-- libc.so.6
> 00007fffa41e0000 64 64 64 r---- libc.so.6
> 00007fffa41f0000 64 64 64 rw--- libc.so.6
> 00007fffa4200000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffa4230000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffa4240000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffa4250000 192 64 0 r-x-- libelf-0.192.so
> 00007fffa4280000 64 64 64 r---- libelf-0.192.so
> 00007fffa4290000 64 0 0 rw--- [ anon ]
> 00007fffa42b0000 256 0 0 r---- [ anon ]
> 00007fffa42f0000 64 64 0 r-x-- [ anon ]
> 00007fffa4300000 320 320 0 r-x-- ld64.so.2
> 00007fffa4350000 64 64 64 r---- ld64.so.2
> 00007fffa4360000 64 64 64 rw--- ld64.so.2
> 00007fffc6880000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13184 3520 1600
> Before uprobe: Page residency = resident
> After uprobe: Page residency = resident
> subtest_nofault:PASS:trigger_uprobe 0 nsec
> subtest_nofault:PASS:res 0 nsec
> FRAME #00: BUILD ID = 4f635d1d48e4f2b67b62a9a07285668cdc85fb18 OFFSET = 2c3f1c
> FRAME #01: BUILD ID = 4f635d1d48e4f2b67b62a9a07285668cdc85fb18 OFFSET = 5a0824
> FRAME #02: BUILD ID = 4f635d1d48e4f2b67b62a9a07285668cdc85fb18 OFFSET = 5a0994
> FRAME #03: BUILD ID = 09139ae1e5cbaf5c598222698e5b8e2e250260b1 OFFSET = 2aba4
> FRAME #04: BUILD ID = 09139ae1e5cbaf5c598222698e5b8e2e250260b1 OFFSET = 2adec
> FRAME #05: BUILD ID = 4f635d1d48e4f2b67b62a9a07285668cdc85fb18 OFFSET = fffffffff0000000
> subtest_nofault:FAIL:build_id_status unexpected build_id_status: actual 1 != expected 2
> #46/1 build_id/nofault-paged-out:FAIL
> #46 build_id:FAIL
>
> Here RSS changes(768 -> 832 -> 768) but looks like page is still
> not getting evicted (as shown "Before uprobe: Page residency = resident")
> after MADV_PAGEOUT and the selftest fails.
>
> 3. But in the very next run page is evicted and selftest passes:
>
> #./test_progs -t build_id/nofault-paged-out
> Entered trigger_uprobe addr -> 0x105b0000
> 145256: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7872 768 64 r-x-- uprobe_multi
> 00000000107b0000 64 64 64 r---- uprobe_multi
> 00000000107c0000 64 64 64 rw--- uprobe_multi
> 00000100317b0000 192 64 64 rw--- [ anon ]
> 00007fffa5cd0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffa5da0000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffa5db0000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffa5dc0000 2304 1280 0 r-x-- libc.so.6
> 00007fffa6000000 64 64 64 r---- libc.so.6
> 00007fffa6010000 64 64 64 rw--- libc.so.6
> 00007fffa6020000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffa6050000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffa6060000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffa6070000 192 64 0 r-x-- libelf-0.192.so
> 00007fffa60a0000 64 64 64 r---- libelf-0.192.so
> 00007fffa60b0000 64 0 0 rw--- [ anon ]
> 00007fffa60d0000 256 0 0 r---- [ anon ]
> 00007fffa6110000 64 64 0 r-x-- [ anon ]
> 00007fffa6120000 320 320 0 r-x-- ld64.so.2
> 00007fffa6170000 64 64 64 r---- ld64.so.2
> 00007fffa6180000 64 64 64 rw--- ld64.so.2
> 00007ffff1890000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13184 3456 896
> 145256: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7872 832 64 r-x-- uprobe_multi
> 00000000107b0000 64 64 64 r---- uprobe_multi
> 00000000107c0000 64 64 64 rw--- uprobe_multi
> 00000100317b0000 192 64 64 rw--- [ anon ]
> 00007fffa5cd0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffa5da0000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffa5db0000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffa5dc0000 2304 1344 0 r-x-- libc.so.6
> 00007fffa6000000 64 64 64 r---- libc.so.6
> 00007fffa6010000 64 64 64 rw--- libc.so.6
> 00007fffa6020000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffa6050000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffa6060000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffa6070000 192 64 0 r-x-- libelf-0.192.so
> 00007fffa60a0000 64 64 64 r---- libelf-0.192.so
> 00007fffa60b0000 64 0 0 rw--- [ anon ]
> 00007fffa60d0000 256 0 0 r---- [ anon ]
> 00007fffa6110000 64 64 0 r-x-- [ anon ]
> 00007fffa6120000 320 320 0 r-x-- ld64.so.2
> 00007fffa6170000 64 64 64 r---- ld64.so.2
> 00007fffa6180000 64 64 64 rw--- ld64.so.2
> 00007ffff1890000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13184 3584 896
> 145256: ./uprobe_multi uprobe-paged-out
> Address Kbytes RSS Dirty Mode Mapping
> 0000000010000000 7872 768 64 r-x-- uprobe_multi
> 00000000107b0000 64 64 64 r---- uprobe_multi
> 00000000107c0000 64 64 64 rw--- uprobe_multi
> 00000100317b0000 192 64 64 rw--- [ anon ]
> 00007fffa5cd0000 832 64 0 r-x-- libzstd.so.1.5.5
> 00007fffa5da0000 64 64 64 r---- libzstd.so.1.5.5
> 00007fffa5db0000 64 64 64 rw--- libzstd.so.1.5.5
> 00007fffa5dc0000 2304 1344 0 r-x-- libc.so.6
> 00007fffa6000000 64 64 64 r---- libc.so.6
> 00007fffa6010000 64 64 64 rw--- libc.so.6
> 00007fffa6020000 192 64 0 r-x-- libz.so.1.3.1.zlib-ng
> 00007fffa6050000 64 64 64 r---- libz.so.1.3.1.zlib-ng
> 00007fffa6060000 64 64 64 rw--- libz.so.1.3.1.zlib-ng
> 00007fffa6070000 192 64 0 r-x-- libelf-0.192.so
> 00007fffa60a0000 64 64 64 r---- libelf-0.192.so
> 00007fffa60b0000 64 0 0 rw--- [ anon ]
> 00007fffa60d0000 256 0 0 r---- [ anon ]
> 00007fffa6110000 64 64 0 r-x-- [ anon ]
> 00007fffa6120000 320 320 0 r-x-- ld64.so.2
> 00007fffa6170000 64 64 64 r---- ld64.so.2
> 00007fffa6180000 64 64 64 rw--- ld64.so.2
> 00007ffff1890000 192 64 64 rw--- [ stack ]
> ---------------- ------- ------- -------
> total kB 13184 3520 896
> Before uprobe: Page residency = paged out
> After uprobe: Page residency = paged out
> #46/1 build_id/nofault-paged-out:OK
> #46 build_id:OK
> #397 stacktrace_build_id:OK
> #398 stacktrace_build_id_nmi:OK
> Summary: 3/1 PASSED, 0 SKIPPED, 0 FAILED
>
> Here it can be seen that page is evicted (as shown
> "Before uprobe: Page residency = paged out").
>
> Although the selftest occasionally passes, its behavior
> remains flaky and unreliable across runs. But introducing
> a sleep before/after both MADV_POPULATE_READ and MADV_PAGEOUT
> tends to improve the consistency with which the selftest passes.
>
> Your valuable suggestions or thoughts on how best to address/debug
> this further would be helpful.
>
How do you check page residency? Instead of just sleeping, I'd add the
code that just waits for the page to be non-resident (with some
reasonable time out in case of bugs), and wait until that condition
happens. (And of course let's increase alignment to 64KB, it has to be
page-aligned across supported architectures).
> Regards,
> Saket
> > > jirka
> > >
> > >
> > > ----
> > > #
> > > # Automatically generated file; DO NOT EDIT.
> > > # Linux/x86 6.10.0 Kernel Configuration
> > > #
> >
> > [...]
> >
