From 47d2db3265f561f899206dfc5c671332af3ab7f2 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Tue, 18 Sep 2018 12:30:18 +1200 Subject: [PATCH] Allow DSM allocation to be interrupted. Chris Travers reported that the startup process can repeatedly try to cancel a backend that is in a posix_fallocate()/EINTR loop and cause it to loop forever. Teach the retry loop to give up if an interrupt is pending. Don't actually check for interrupts in that loop though, because a non-local exit would skip some clean-up code in the caller. Back-patch to 9.4 where DSM was added (and posix_fallocate() was later back-patched). Author: Chris Travers Reviewed-by: Ildar Musin, Murak Kabilov, Oleksii Kliukin Tested-by: Oleksii Kliukin Discussion: https://postgr.es/m/CAN-RpxB-oeZve_J3SM_6%3DHXPmvEG%3DHX%2B9V9pi8g2YR7YW0rBBg%40mail.gmail.com --- src/backend/storage/ipc/dsm_impl.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c index 77e1bab54b..70f899e765 100644 --- a/src/backend/storage/ipc/dsm_impl.c +++ b/src/backend/storage/ipc/dsm_impl.c @@ -47,6 +47,7 @@ */ #include "postgres.h" +#include "miscadmin.h" #include #include @@ -330,6 +331,14 @@ dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size, shm_unlink(name); errno = save_errno; + /* + * If we received a query cancel or termination signal, we will have + * EINTR set here. If the caller said that errors are OK here, check + * for interrupts immediately. + */ + if (errno == EINTR && elevel >= ERROR) + CHECK_FOR_INTERRUPTS(); + ereport(elevel, (errcode_for_dynamic_shared_memory(), errmsg("could not resize shared memory segment \"%s\" to %zu bytes: %m", @@ -419,11 +428,15 @@ dsm_impl_posix_resize(int fd, off_t size) #if defined(HAVE_POSIX_FALLOCATE) && defined(__linux__) if (rc == 0) { - /* We may get interrupted, if so just retry. */ + /* + * We may get interrupted. If so, just retry unless there is an + * interrupt pending. This avoids the possibility of looping forever + * if another backend is repeatedly trying to interrupt us. + */ do { rc = posix_fallocate(fd, 0, size); - } while (rc == EINTR); + } while (rc == EINTR && !(ProcDiePending || QueryCancelPending)); /* * The caller expects errno to be set, but posix_fallocate() doesn't -- 2.17.0