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Commit597f669

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injection_points: Fix incorrect spinlock acquisition
Injection points created under injection_points_set_local() are cleanedup by a shmem_exit() callback. The spinlock used by the module wouldbe hold while calling InjectionPointDetach(), which is incorrect asspinlocks should avoid external calls while hold.This commit changes the shmem_exit() callback to detach the points inthree steps with the spinlock acquired twice, knowing that theinjection points should be around with the conditions related to them:- Scans for the points to detach in a first loop, while holding thespinlock.- Detach them.- Remove the registered conditions.It is still possible for other processes to detach local pointsconcurrently of the callback. I have wanted to restrict the detach, butNoah has mentioned that he has in mind some cases that may require thiscapability. No tests in the tree based on injection points need thatcurrently.Thinko inf587338.Reported-by: Noah MischReviewed-by: Noah MischDiscussion:https://postgr.es/m/20240501231214.40@rfd.leadboat.com
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‎src/test/modules/injection_points/injection_points.c

Lines changed: 29 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -159,10 +159,39 @@ injection_point_allowed(const char *name)
159159
staticvoid
160160
injection_points_cleanup(intcode,Datumarg)
161161
{
162+
charnames[INJ_MAX_CONDITION][INJ_NAME_MAXLEN]= {0};
163+
intcount=0;
164+
162165
/* Leave if nothing is tracked locally */
163166
if (!injection_point_local)
164167
return;
165168

169+
/*
170+
* This is done in three steps: detect the points to detach, detach them
171+
* and release their conditions.
172+
*/
173+
SpinLockAcquire(&inj_state->lock);
174+
for (inti=0;i<INJ_MAX_CONDITION;i++)
175+
{
176+
InjectionPointCondition*condition=&inj_state->conditions[i];
177+
178+
if (condition->name[0]=='\0')
179+
continue;
180+
181+
if (condition->pid!=MyProcPid)
182+
continue;
183+
184+
/* Extract the point name to detach */
185+
strlcpy(names[count],condition->name,INJ_NAME_MAXLEN);
186+
count++;
187+
}
188+
SpinLockRelease(&inj_state->lock);
189+
190+
/* Detach, without holding the spinlock */
191+
for (inti=0;i<count;i++)
192+
InjectionPointDetach(names[i]);
193+
194+
/* Clear all the conditions */
166195
SpinLockAcquire(&inj_state->lock);
167196
for (inti=0;i<INJ_MAX_CONDITION;i++)
168197
{
@@ -174,8 +203,6 @@ injection_points_cleanup(int code, Datum arg)
174203
if (condition->pid!=MyProcPid)
175204
continue;
176205

177-
/* Detach the injection point and unregister condition */
178-
InjectionPointDetach(condition->name);
179206
condition->name[0]='\0';
180207
condition->pid=0;
181208
}

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