[PATCH 0/2] reftable/stack: fix race in up-to-date check

Hi,

In 6fdfaf15 (reftable/stack: use stat info to avoid re-reading stack list, 2024-01-11) we have introduced a new mechanism to avoid re-reading the table list in case stat(3P) figures out that the stack didn't change since the last time we read it.

Unfortunately, I've been able to hit a bug there that can happen under very specific circumstances when a reading and writing process race with each other. When the writer appends to the stack and then compacts it, it may happen that we recycle the previously-used inode of "tables.list" so that the resulting `struct stat` exactly matches the cached value of the reading process.

The first patch is merely cosmetic, whereas the second patch fixes the described race. The topic depends on ps/reftable-optimize-io, which has introduced the issue.

Patrick

Patrick Steinhardt (2):
  reftable/stack: unconditionally reload stack after commit
  reftable/stack: fix race in up-to-date check

 reftable/stack.c  | 101 ++++++++++++++++++++++++++++++++++++++++++----
 reftable/stack.h  |   4 +-
 reftable/system.h |   1 -
 3 files changed, 96 insertions(+), 10 deletions(-)

base-commit: 718a93ecc06ed59dda4e6a5d91b1c2169275694f