7:33 a.m.
For the following scenario:
Starting state for mde_flags -> TRUST_CONTENT and TRUST_DIR_CHUNKS
Thread 2 waiting for a READ LOCK
Thread 1 has a WRITE LOCK - results in clearing the TRUST_CONTENT flag and releases the
lock
Thread 2 acquires the READ LOCK -- TRUST_CONTENT is clear, but this thread assumes that
TRUST_CONTENT is true (state before it waiting on the locks).
Is the rest of the mdcache_readdir_chunked code still safe to continue? Can the result
from mdcache_avl_lookup_ck be depended on?
Thanks,
Vandana
On 6/24/19, 5:50 AM, "Daniel Gryniewicz" <dang(a)redhat.com> wrote:
It should be safe. Testing the flags is atomic, so that part is safe,
and the worst that happens is we invalidate twice, so it's still correct.
Daniel
On 6/20/19 11:46 AM, Rungta, Vandana wrote:
A separate but related question:
In mdcache_readdir_chunked towards the beginning where mde_flags are tested for
MDCACHE_TRUST_CONTENT | MDCACHE_TRUST_DIR_CHUNKS, the test is done outside the lock. It
is possible that the flags indicate that the directory content can be trusted and while
waiting for a READ_LOCK, the thread holding the WRITE_LOCK can invalidate the content. Do
the flags need to be checked after obtaining the lock and when upgrading the lock from
read to write?