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hlinnakahlinnaka
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Move cancel key generation to after forking the backend
Move responsibility of generating the cancel key to the backend process. The cancel key is now generated after forking, and the backend advertises it in the ProcSignal array. When a cancel request arrives, the backend handling it scans the ProcSignal array to find the target pid and cancel key. This is similar to how this previously worked in the EXEC_BACKEND case with the ShmemBackendArray, just reusing the ProcSignal array. One notable change is that we no longer generate cancellation keys for non-backend processes. We generated them before just to prevent a malicious user from canceling them; the keys for non-backend processes were never actually given to anyone. There is now an explicit flag indicating whether a process has a valid key or not. I wrote this originally in preparation for supporting longer cancel keys, but it's a nice cleanup on its own. Reviewed-by: Jelte Fennema-Nio Discussion: https://www.postgresql.org/message-id/508d0505-8b7a-4864-a681-e7e5edfe32aa@iki.fi
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12 files changed

+193
-262
lines changed

12 files changed

+193
-262
lines changed

‎src/backend/postmaster/auxprocess.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -71,7 +71,7 @@ AuxiliaryProcessMainCommon(void)
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7272
BaseInit();
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74-
ProcSignalInit();
74+
ProcSignalInit(false, 0);
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/*
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* Auxiliary processes don't run transactions, but they may need a

‎src/backend/postmaster/launch_backend.c

Lines changed: 4 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -58,6 +58,7 @@
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#include "storage/pg_shmem.h"
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#include "storage/pmsignal.h"
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#include "storage/proc.h"
61+
#include "storage/procsignal.h"
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#include "tcop/backend_startup.h"
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#include "tcop/tcopprot.h"
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#include "utils/builtins.h"
@@ -94,7 +95,6 @@ typedef int InheritableSocket;
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typedef struct
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{
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char DataDir[MAXPGPATH];
97-
int32 MyCancelKey;
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int MyPMChildSlot;
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#ifndef WIN32
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unsigned long UsedShmemSegID;
@@ -104,7 +104,6 @@ typedef struct
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#endif
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void *UsedShmemSegAddr;
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slock_t *ShmemLock;
107-
struct bkend *ShmemBackendArray;
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#ifdef USE_INJECTION_POINTS
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struct InjectionPointsCtl *ActiveInjectionPoints;
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#endif
@@ -119,6 +118,7 @@ typedef struct
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PGPROC *AuxiliaryProcs;
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PGPROC *PreparedXactProcs;
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volatile PMSignalData *PMSignalState;
121+
ProcSignalHeader *ProcSignal;
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pid_t PostmasterPid;
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TimestampTz PgStartTime;
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TimestampTz PgReloadTime;
@@ -702,7 +702,6 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
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703703
strlcpy(param->DataDir, DataDir, MAXPGPATH);
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705-
param->MyCancelKey = MyCancelKey;
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param->MyPMChildSlot = MyPMChildSlot;
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#ifdef WIN32
@@ -712,7 +711,6 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
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param->UsedShmemSegAddr = UsedShmemSegAddr;
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param->ShmemLock = ShmemLock;
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param->ShmemBackendArray = ShmemBackendArray;
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717715
#ifdef USE_INJECTION_POINTS
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param->ActiveInjectionPoints = ActiveInjectionPoints;
@@ -729,6 +727,7 @@ save_backend_variables(BackendParameters *param, ClientSocket *client_sock,
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param->AuxiliaryProcs = AuxiliaryProcs;
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param->PreparedXactProcs = PreparedXactProcs;
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param->PMSignalState = PMSignalState;
730+
param->ProcSignal = ProcSignal;
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param->PostmasterPid = PostmasterPid;
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param->PgStartTime = PgStartTime;
@@ -965,7 +964,6 @@ restore_backend_variables(BackendParameters *param)
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SetDataDir(param->DataDir);
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968-
MyCancelKey = param->MyCancelKey;
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MyPMChildSlot = param->MyPMChildSlot;
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971969
#ifdef WIN32
@@ -975,7 +973,6 @@ restore_backend_variables(BackendParameters *param)
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UsedShmemSegAddr = param->UsedShmemSegAddr;
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ShmemLock = param->ShmemLock;
978-
ShmemBackendArray = param->ShmemBackendArray;
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#ifdef USE_INJECTION_POINTS
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ActiveInjectionPoints = param->ActiveInjectionPoints;
@@ -992,6 +989,7 @@ restore_backend_variables(BackendParameters *param)
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AuxiliaryProcs = param->AuxiliaryProcs;
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PreparedXactProcs = param->PreparedXactProcs;
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PMSignalState = param->PMSignalState;
992+
ProcSignal = param->ProcSignal;
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996994
PostmasterPid = param->PostmasterPid;
997995
PgStartTime = param->PgStartTime;

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