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Avoid calling sqlite3BtreeEnter() in a corner case where the corresponding database handle mutex (sqlite3.mutex) may not be held. This prevents a potential deadlock or crash that can occur if the backup API, shared-cache mode and SQLITE_HAVE_CODEC are all in use.

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FossilOrigin-Name: 89b8c377a6f03d9fa885f3f94c1f0b1eec263dea
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dan
2012-09-28 20:23:42 +00:00
parent 70a1b71fb6
commit 0094f37e1f
5 changed files with 32 additions and 12 deletions
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16
src/btree.c
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@@ -2200,6 +2200,22 @@ int sqlite3BtreeGetPageSize(Btree *p){
return p->pBt->pageSize;
}
/*
** This function is similar to sqlite3BtreeGetReserve(), except that it
** may only be called if it is guaranteed that the b-tree mutex is already
** held.
**
** This is useful in one special case in the backup API code where it is
** known that the shared b-tree mutex is held, but the mutex on the
** database handle that owns *p is not. In this case if sqlite3BtreeEnter()
** were to be called, it might collide with some other operation on the
** database handle that owns *p, causing undefined behaviour.
*/
int sqlite3BtreeGetReserveNoMutex(Btree *p){
assert( sqlite3_mutex_held(p->pBt->mutex) );
return p->pBt->pageSize - p->pBt->usableSize;
}
#if !defined(SQLITE_OMIT_PAGER_PRAGMAS) || !defined(SQLITE_OMIT_VACUUM)
/*
** Return the number of bytes of space at the end of every page that