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Race condition between spa async threads and export

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In the past we've seen multiple race conditions that have
to do with open-context threads async threads and concurrent
calls to spa_export()/spa_destroy() (including the one
referenced in issue #9015).

This patch ensures that only one thread can execute the
main body of spa_export_common() at a time, with subsequent
threads returning with a new error code created just for
this situation, eliminating this way any race condition
bugs introduced by concurrent calls to this function.

Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Closes #9015 
Closes #9044
This commit is contained in:
Serapheim Dimitropoulos
2019-07-18 13:02:33 -07:00
committed by Brian Behlendorf
parent 1c44a5c97f
commit 43a8536260
6 changed files with 42 additions and 2 deletions
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module/zfs/spa.c
+17 -1
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@@ -5790,6 +5790,13 @@ spa_export_common(char *pool, int new_state, nvlist_t **oldconfig,
return (SET_ERROR(ENOENT));
}
if (spa->spa_is_exporting) {
/* the pool is being exported by another thread */
mutex_exit(&spa_namespace_lock);
return (SET_ERROR(ZFS_ERR_EXPORT_IN_PROGRESS));
}
spa->spa_is_exporting = B_TRUE;
/*
* Put a hold on the pool, drop the namespace lock, stop async tasks,
* reacquire the namespace lock, and see if we can export.
@@ -5825,6 +5832,7 @@ spa_export_common(char *pool, int new_state, nvlist_t **oldconfig,
(spa->spa_inject_ref != 0 &&
new_state != POOL_STATE_UNINITIALIZED)) {
spa_async_resume(spa);
spa->spa_is_exporting = B_FALSE;
mutex_exit(&spa_namespace_lock);
return (SET_ERROR(EBUSY));
}
@@ -5839,6 +5847,7 @@ spa_export_common(char *pool, int new_state, nvlist_t **oldconfig,
if (!force && new_state == POOL_STATE_EXPORTED &&
spa_has_active_shared_spare(spa)) {
spa_async_resume(spa);
spa->spa_is_exporting = B_FALSE;
mutex_exit(&spa_namespace_lock);
return (SET_ERROR(EXDEV));
}
@@ -5890,9 +5899,16 @@ export_spa:
if (!hardforce)
spa_write_cachefile(spa, B_TRUE, B_TRUE);
spa_remove(spa);
} else {
/*
* If spa_remove() is not called for this spa_t and
* there is any possibility that it can be reused,
* we make sure to reset the exporting flag.
*/
spa->spa_is_exporting = B_FALSE;
}
mutex_exit(&spa_namespace_lock);
mutex_exit(&spa_namespace_lock);
return (0);
}