tree bb2c6fe5e7b2308eb04ee30c8fb1738d71517aa5
parent f0b4f657448c198d3e4549fdd3d29b65b3e37155
author Olivier Houchard <cognet@ci0.org> 1584542909 +0100
committer Willy Tarreau <w@1wt.eu> 1585673844 +0200
encoding latin1

MINOR: memory: Change the flush_lock to a spinlock, and don't get it in alloc.

The flush_lock was introduced, mostly to be sure that pool_gc() will never
dereference a pointer that has been free'd. __pool_get_first() was acquiring
the lock to, the fear was that otherwise that pointer could get free'd later,
and then pool_gc() would attempt to dereference it. However, that can not
happen, because the only functions that can free a pointer, when using
lockless pools, are pool_gc() and pool_flush(), and as long as those two
are mutually exclusive, nobody will be able to free the pointer while
pool_gc() attempts to access it.
So change the flush_lock to a spinlock, and don't bother acquire/release
it in __pool_get_first(), that way callers of __pool_get_first() won't have
to wait while the pool is flushed. The worst that can happen is we call
__pool_refill_alloc() while the pool is getting flushed, and memory can
get allocated just to be free'd.

This may help with github issue #552

This may be backported to 2.1, 2.0 and 1.9.

(cherry picked from commit 899fb8abdcda90e3b3c69f6945f83c4c1107c459)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 635c9a85464dacacae6ac20d4b8082288f7fbbd1)
Signed-off-by: Willy Tarreau <w@1wt.eu>