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Allow DSM allocation to be interrupted.

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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, Murat Kabilov, Oleksii Kliukin
Tested-by: Oleksii Kliukin
Discussion: https://postgr.es/m/CAN-RpxB-oeZve_J3SM_6%3DHXPmvEG%3DHX%2B9V9pi8g2YR7YW0rBBg%40mail.gmail.com
This commit is contained in:
Thomas Munro 2018-09-18 22:56:36 +12:00
parent 1d6fbc38d9
commit 422952ee78
1 changed files with 15 additions and 2 deletions
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17
src/backend/storage/ipc/dsm_impl.c
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@ -47,6 +47,7 @@
*/
#include "postgres.h"
#include "miscadmin.h"
#include <fcntl.h>
#include <unistd.h>
@ -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