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| author | Thomas Munro <tmunro@postgresql.org> | 2019-02-18 09:53:26 +1300 |
|---|---|---|
| committer | Thomas Munro <tmunro@postgresql.org> | 2019-02-18 09:59:27 +1300 |
| commit | 1d93d180454f9da74677dd0498f5408efe6b603d (patch) | |
| tree | 291787be2f32fb4e947db144e7b00fa881dff51a | |
| parent | 7f39f0344129706979174ba530f8cc21b7d9f4a3 (diff) | |
| download | postgresql-1d93d180454f9da74677dd0498f5408efe6b603d.tar.gz postgresql-1d93d180454f9da74677dd0498f5408efe6b603d.zip | |
Fix race in dsm_unpin_segment() when handles are reused.
Teach dsm_unpin_segment() to skip segments that are in the process
of being destroyed by another backend, when searching for a handle.
Such a segment cannot possibly be the one we are looking for, even
if its handle matches. Another slot might hold a recently created
segment that has the same handle value by coincidence, and we need
to keep searching for that one.
The bug caused rare "cannot unpin a segment that is not pinned"
errors on 10 and 11. Similar to commit 6c0fb941 for dsm_attach().
Back-patch to 10, where dsm_unpin_segment() landed.
Author: Thomas Munro
Reported-by: Justin Pryzby
Tested-by: Justin Pryzby (along with other recent DSA/DSM fixes)
Discussion: https://postgr.es/m/20190216023854.GF30291@telsasoft.com
| -rw-r--r-- | src/backend/storage/ipc/dsm.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c index fde420d6edb..ef509d99b5d 100644 --- a/src/backend/storage/ipc/dsm.c +++ b/src/backend/storage/ipc/dsm.c @@ -891,8 +891,8 @@ dsm_unpin_segment(dsm_handle handle) LWLockAcquire(DynamicSharedMemoryControlLock, LW_EXCLUSIVE); for (i = 0; i < dsm_control->nitems; ++i) { - /* Skip unused slots. */ - if (dsm_control->item[i].refcnt == 0) + /* Skip unused slots and segments that are concurrently going away. */ + if (dsm_control->item[i].refcnt <= 1) continue; /* If we've found our handle, we can stop searching. */ |