[00/14] namei: clean up retry logic in various do_* functions

Message

Dmitry Kadashev July 15, 2021, 10:35 a.m. UTC

Suggested by Linus in https://lore.kernel.org/io-uring/CAHk-=wh=cpt_tQCirzFZRPawRpbuFTZ2MxNpXiyUF+eBXF=[e-mail]/

This patchset does all the do_* functions one by one. The idea is to
move the main logic to a helper function and handle stale retries /
struct filename cleanups outside, which makes the logic easier to
follow.

There are a few minor changes in behavior:

1. filename_lookup() / filename_parentat() / filename_create() do their
own retries on ESTALE (regardless of flags), and previously they were
exempt from retries in the do_* functions (but they *were* called on
retry - it's just the return code wasn't checked for ESTALE). And
now the retry is done on the upper level, and so technically it could be
called a behavior change. Hopefully it's an edge case where an
additional check does not matter.

2. Some safety checks like may_mknod() / flags validation are now
repeated on retry. Those are mostly trivial and retry is a slow path, so
that should be OK.

3. retry_estale() is wrapped into unlikely() now

On top of https://lore.kernel.org/io-uring/[e-mail]/

v2:

- Split flow changes and code reorganization to different commits;

- Move more checks into the new helpers, to avoid gotos in the touched
  do_* functions completely;

- Add unlikely() around retry_estale();

- Name the new helper functions try_* instead of *_helper;

Dmitry Kadashev (14):
  namei: prepare do_rmdir for refactoring
  namei: clean up do_rmdir retry logic
  namei: prepare do_unlinkat for refactoring
  namei: clean up do_unlinkat retry logic
  namei: prepare do_mkdirat for refactoring
  namei: clean up do_mkdirat retry logic
  namei: prepare do_mknodat for refactoring
  namei: clean up do_mknodat retry logic
  namei: prepare do_symlinkat for refactoring
  namei: clean up do_symlinkat retry logic
  namei: prepare do_linkat for refactoring
  namei: clean up do_linkat retry logic
  namei: prepare do_renameat2 for refactoring
  namei: clean up do_renameat2 retry logic

 fs/namei.c | 252 +++++++++++++++++++++++++++++------------------------
 1 file changed, 140 insertions(+), 112 deletions(-)

Comments

Dmitry Kadashev July 15, 2021, 10:39 a.m. UTC | #1

On Thu, Jul 15, 2021 at 5:36 PM Dmitry Kadashev <[e-mail]> wrote:
>
> Suggested by Linus in https://lore.kernel.org/io-uring/CAHk-=wh=cpt_tQCirzFZRPawRpbuFTZ2MxNpXiyUF+eBXF=[e-mail]/
>
> This patchset does all the do_* functions one by one. The idea is to
> move the main logic to a helper function and handle stale retries /
> struct filename cleanups outside, which makes the logic easier to
> follow.
>
> There are a few minor changes in behavior:
>
> 1. filename_lookup() / filename_parentat() / filename_create() do their
> own retries on ESTALE (regardless of flags), and previously they were
> exempt from retries in the do_* functions (but they *were* called on
> retry - it's just the return code wasn't checked for ESTALE). And
> now the retry is done on the upper level, and so technically it could be
> called a behavior change. Hopefully it's an edge case where an
> additional check does not matter.
>
> 2. Some safety checks like may_mknod() / flags validation are now
> repeated on retry. Those are mostly trivial and retry is a slow path, so
> that should be OK.
>
> 3. retry_estale() is wrapped into unlikely() now
>
> On top of https://lore.kernel.org/io-uring/[e-mail]/
>
> v2:
>
> - Split flow changes and code reorganization to different commits;
>
> - Move more checks into the new helpers, to avoid gotos in the touched
>   do_* functions completely;
>
> - Add unlikely() around retry_estale();
>
> - Name the new helper functions try_* instead of *_helper;
>
> Dmitry Kadashev (14):
>   namei: prepare do_rmdir for refactoring
>   namei: clean up do_rmdir retry logic
>   namei: prepare do_unlinkat for refactoring
>   namei: clean up do_unlinkat retry logic
>   namei: prepare do_mkdirat for refactoring
>   namei: clean up do_mkdirat retry logic
>   namei: prepare do_mknodat for refactoring
>   namei: clean up do_mknodat retry logic
>   namei: prepare do_symlinkat for refactoring
>   namei: clean up do_symlinkat retry logic
>   namei: prepare do_linkat for refactoring
>   namei: clean up do_linkat retry logic
>   namei: prepare do_renameat2 for refactoring
>   namei: clean up do_renameat2 retry logic
>
>  fs/namei.c | 252 +++++++++++++++++++++++++++++------------------------
>  1 file changed, 140 insertions(+), 112 deletions(-)

Ooops, the subject misses "v2", I'll resend.