Re: [vfs] 8bb3c61baf: vm-scalability.median -23.7% regression

Hugh Dickins
2019-09-09T03:10:37Z

On Mon, 9 Sep 2019, Al Viro wrote:
> On Sun, Sep 08, 2019 at 10:46:01PM +0100, Al Viro wrote:
> > On Tue, Sep 03, 2019 at 04:41:22PM +0800, kernel test robot wrote:
> > > Greeting,
> > >
> > > FYI, we noticed a -23.7% regression of vm-scalability.median due to commit:
> > >
> > >
> > > commit: 8bb3c61bafa8c1cd222ada602bb94ff23119e738 ("vfs: Convert ramfs, shmem, tmpfs, devtmpfs, rootfs to use the new mount API")
> > > https://kernel.googlesource.com/pub/scm/linux/kernel/git/viro/vfs.git work.mount
> > >
> > > in testcase: vm-scalability
> > > on test machine: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with 128G memory
> > > with following parameters:
> > >
> > > runtime: 300s
> > > size: 16G
> > > test: shm-pread-rand
> > > cpufreq_governor: performance
> > > ucode: 0xb000036
> >
> > That thing loses size=... option. Both size= and nr_blocks= affect the
> > same thing (->max_blocks), but the parser keeps track of the options
> > it has seen and applying the parsed data to superblock checks only
> > whether nr_blocks= had been there. IOW, size= gets parsed, but the
> > result goes nowhere.
> >
> > I'm not sure whether it's better to fix the patch up or redo it from
> > scratch - it needs to be carved up anyway and it's highly non-transparent,
> > so I'm probably going to replace the damn thing entirely with something
> > that would be easier to follow.
>
> ... and this
> + { Opt_huge, "deny", SHMEM_HUGE_DENY },
> + { Opt_huge, "force", SHMEM_HUGE_FORCE },
> had been wrong - huge=deny and huge=force should not be accepted _and_
> fs_parameter_enum is not suitable for negative constants right now
> anyway.

Sorry you've been spending time redisovering these, Al: I sent David
the tmpfs fixes (Cc'ing you and Andrew and lists) a couple of weeks
ago - but had no idea until your mail that the "loss of size" was
behind this vm-scalability regression report.

Ah, not for the first time, I missed saying "[PATCH]" in the subject:
sorry, that may have rendered it invisible to many eyes.

Here's what Andrew has been carrying in the mmotm tree since I sent it:
I'm sure we'd both be happy for you to take it into your tree. I had
expected it to percolate through from mmotm to linux-next by now,
but apparently not.

From: Hugh Dickins <hughd@google.com>
Subject: tmpfs: fixups to use of the new mount API

Several fixups to shmem_parse_param() and tmpfs use of new mount API:

mm/shmem.c manages filesystem named "tmpfs": revert "shmem" to "tmpfs"
in its mount error messages.

/sys/kernel/mm/transparent_hugepage/shmem_enabled has valid options
"deny" and "force", but they are not valid as tmpfs "huge" options.

The "size" param is an alternative to "nr_blocks", and needs to be
recognized as changing max_blocks. And where there's ambiguity, it's
better to mention "size" than "nr_blocks" in messages, since "size" is
the variant shown in /proc/mounts.

shmem_apply_options() left ctx->mpol as the new mpol, so then it was
freed in shmem_free_fc(), and the filesystem went on to use-after-free.

shmem_parse_param() issue "tmpfs: Bad value for '%s'" messages just
like fs_parse() would, instead of a different wording. Where config
disables "mpol" or "huge", say "tmpfs: Unsupported parameter '%s'".

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1908191503290.1253@eggly.anvils
Fixes: 144df3b288c41 ("vfs: Convert ramfs, shmem, tmpfs, devtmpfs, rootfs to use the new mount API")
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/shmem.c | 80 ++++++++++++++++++++++++++-------------------------
1 file changed, 42 insertions(+), 38 deletions(-)

--- a/mm/shmem.c~tmpfs-fixups-to-use-of-the-new-mount-api
+++ a/mm/shmem.c
@@ -3432,13 +3432,11 @@ static const struct fs_parameter_enum sh
{ Opt_huge, "always", SHMEM_HUGE_ALWAYS },
{ Opt_huge, "within_size", SHMEM_HUGE_WITHIN_SIZE },
{ Opt_huge, "advise", SHMEM_HUGE_ADVISE },
- { Opt_huge, "deny", SHMEM_HUGE_DENY },
- { Opt_huge, "force", SHMEM_HUGE_FORCE },
{}
};

const struct fs_parameter_description shmem_fs_parameters = {
- .name = "shmem",
+ .name = "tmpfs",
.specs = shmem_param_specs,
.enums = shmem_param_enums,
};
@@ -3448,9 +3446,9 @@ static void shmem_apply_options(struct s
unsigned long inodes_in_use)
{
struct shmem_fs_context *ctx = fc->fs_private;
- struct mempolicy *old = NULL;

- if (test_bit(Opt_nr_blocks, &ctx->changes))
+ if (test_bit(Opt_nr_blocks, &ctx->changes) ||
+ test_bit(Opt_size, &ctx->changes))
sbinfo->max_blocks = ctx->max_blocks;
if (test_bit(Opt_nr_inodes, &ctx->changes)) {
sbinfo->max_inodes = ctx->max_inodes;
@@ -3459,8 +3457,11 @@ static void shmem_apply_options(struct s
if (test_bit(Opt_huge, &ctx->changes))
sbinfo->huge = ctx->huge;
if (test_bit(Opt_mpol, &ctx->changes)) {
- old = sbinfo->mpol;
- sbinfo->mpol = ctx->mpol;
+ /*
+ * Update sbinfo->mpol now while stat_lock is held.
+ * Leave shmem_free_fc() to free the old mpol if any.
+ */
+ swap(sbinfo->mpol, ctx->mpol);
}

if (fc->purpose != FS_CONTEXT_FOR_RECONFIGURE) {
@@ -3471,8 +3472,6 @@ static void shmem_apply_options(struct s
if (test_bit(Opt_mode, &ctx->changes))
sbinfo->mode = ctx->mode;
}
-
- mpol_put(old);
}

static int shmem_parse_param(struct fs_context *fc, struct fs_parameter *param)
@@ -3498,7 +3497,7 @@ static int shmem_parse_param(struct fs_c
rest++;
}
if (*rest)
- return invalf(fc, "shmem: Invalid size");
+ goto bad_value;
ctx->max_blocks = DIV_ROUND_UP(size, PAGE_SIZE);
break;

@@ -3506,55 +3505,59 @@ static int shmem_parse_param(struct fs_c
rest = param->string;
ctx->max_blocks = memparse(param->string, &rest);
if (*rest)
- return invalf(fc, "shmem: Invalid nr_blocks");
+ goto bad_value;
break;
+
case Opt_nr_inodes:
rest = param->string;
ctx->max_inodes = memparse(param->string, &rest);
if (*rest)
- return invalf(fc, "shmem: Invalid nr_inodes");
+ goto bad_value;
break;
+
case Opt_mode:
ctx->mode = result.uint_32 & 07777;
break;
+
case Opt_uid:
ctx->uid = make_kuid(current_user_ns(), result.uint_32);
if (!uid_valid(ctx->uid))
- return invalf(fc, "shmem: Invalid uid");
+ goto bad_value;
break;

case Opt_gid:
ctx->gid = make_kgid(current_user_ns(), result.uint_32);
if (!gid_valid(ctx->gid))
- return invalf(fc, "shmem: Invalid gid");
+ goto bad_value;
break;

case Opt_huge:
-#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
- if (!has_transparent_hugepage() &&
- result.uint_32 != SHMEM_HUGE_NEVER)
- return invalf(fc, "shmem: Huge pages disabled");
-
ctx->huge = result.uint_32;
+ if (ctx->huge != SHMEM_HUGE_NEVER &&
+ !(IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
+ has_transparent_hugepage()))
+ goto unsupported_parameter;
break;
-#else
- return invalf(fc, "shmem: huge= option disabled");
-#endif
-
- case Opt_mpol: {
-#ifdef CONFIG_NUMA
- struct mempolicy *mpol;
- if (mpol_parse_str(param->string, &mpol))
- return invalf(fc, "shmem: Invalid mpol=");
- mpol_put(ctx->mpol);
- ctx->mpol = mpol;
-#endif
- break;
- }
+
+ case Opt_mpol:
+ if (IS_ENABLED(CONFIG_NUMA)) {
+ struct mempolicy *mpol;
+ if (mpol_parse_str(param->string, &mpol))
+ goto bad_value;
+ mpol_put(ctx->mpol);
+ ctx->mpol = mpol;
+ break;
+ }
+ goto unsupported_parameter;
}

__set_bit(opt, &ctx->changes);
return 0;
+
+unsupported_parameter:
+ return invalf(fc, "tmpfs: Unsupported parameter '%s'", param->key);
+bad_value:
+ return invalf(fc, "tmpfs: Bad value for '%s'", param->key);
}

/*
@@ -3572,14 +3575,15 @@ static int shmem_reconfigure(struct fs_c
unsigned long inodes_in_use;

spin_lock(&sbinfo->stat_lock);
- if (test_bit(Opt_nr_blocks, &ctx->changes)) {
+ if (test_bit(Opt_nr_blocks, &ctx->changes) ||
+ test_bit(Opt_size, &ctx->changes)) {
if (ctx->max_blocks && !sbinfo->max_blocks) {
spin_unlock(&sbinfo->stat_lock);
- return invalf(fc, "shmem: Can't retroactively limit nr_blocks");
+ return invalf(fc, "tmpfs: Cannot retroactively limit size");
}
if (percpu_counter_compare(&sbinfo->used_blocks, ctx->max_blocks) > 0) {
spin_unlock(&sbinfo->stat_lock);
- return invalf(fc, "shmem: Too few blocks for current use");
+ return invalf(fc, "tmpfs: Too small a size for current use");
}
}

@@ -3587,11 +3591,11 @@ static int shmem_reconfigure(struct fs_c
if (test_bit(Opt_nr_inodes, &ctx->changes)) {
if (ctx->max_inodes && !sbinfo->max_inodes) {
spin_unlock(&sbinfo->stat_lock);
- return invalf(fc, "shmem: Can't retroactively limit nr_inodes");
+ return invalf(fc, "tmpfs: Cannot retroactively limit inodes");
}
if (ctx->max_inodes < inodes_in_use) {
spin_unlock(&sbinfo->stat_lock);
- return invalf(fc, "shmem: Too few inodes for current use");
+ return invalf(fc, "tmpfs: Too few inodes for current use");
}
}

_