Consistently enforce the restriction against calling malloc/free when in a
critical section. uma_zalloc_arg()/uma_zalloc_free() may acquire a sleepable lock on the zone. The malloc() family of functions may call uma_zalloc_arg() or uma_zalloc_free(). The malloc(9) man page currently claims that free() will never sleep. It also implies that the malloc() family of functions will not sleep when called with M_NOWAIT. However, it is more correct to say that these functions will not sleep indefinitely. Indeed, they may acquire a sleepable lock. However, a developer may overlook this restriction because the WITNESS check that catches attempts to call the malloc() family of functions within a critical section is inconsistenly applied. This change clarifies the language of the malloc(9) man page to clarify the restriction against calling the malloc() family of functions while in a critical section or holding a spin lock. It also adds KASSERTs at appropriate points to make the enforcement of this restriction more consistent. PR: 204633 Differential Revision: https://reviews.freebsd.org/D4197 Reviewed by: markj Approved by: gnn (mentor) Sponsored by: Juniper Networks
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2020-12-20 02:59:44 +00:00
svn path=/head/; revision=291074
@ -29,7 +29,7 @@
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.\" $NetBSD: malloc.9,v 1.3 1996/11/11 00:05:11 lukem Exp $
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.\" $FreeBSD$
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.\"
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.Dd January 16, 2014
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.Dd November 19, 2015
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.Dt MALLOC 9
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.Os
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.Sh NAME
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@ -227,6 +227,13 @@ may sleep when called with
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.Dv M_WAITOK .
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.Fn free
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never sleeps.
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However,
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.Fn malloc ,
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.Fn realloc,
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.Fn reallocf
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and
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.Fn free
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may not be called in a critical section or while holding a spin lock.
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.Pp
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Any calls to
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.Fn malloc
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@ -476,6 +476,9 @@ malloc(unsigned long size, struct malloc_type *mtp, int flags)
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KASSERT(curthread->td_intr_nesting_level == 0,
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("malloc(M_WAITOK) in interrupt context"));
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KASSERT(curthread->td_critnest == 0,
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("malloc: called with spinlock or critical section held"));
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#ifdef DEBUG_MEMGUARD
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if (memguard_cmp_mtp(mtp, size)) {
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va = memguard_alloc(size, flags);
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@ -542,6 +545,9 @@ free(void *addr, struct malloc_type *mtp)
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KASSERT(mtp->ks_magic == M_MAGIC, ("free: bad malloc type magic"));
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KASSERT(curthread->td_critnest == 0,
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("free: called with spinlock or critical section held"));
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/* free(NULL, ...) does nothing */
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if (addr == NULL)
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return;
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@ -605,6 +611,9 @@ realloc(void *addr, unsigned long size, struct malloc_type *mtp, int flags)
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KASSERT(mtp->ks_magic == M_MAGIC,
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("realloc: bad malloc type magic"));
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KASSERT(curthread->td_critnest == 0,
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("realloc: called with spinlock or critical section held"));
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/* realloc(NULL, ...) is equivalent to malloc(...) */
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if (addr == NULL)
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return (malloc(size, mtp, flags));
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@ -2149,6 +2149,10 @@ uma_zalloc_arg(uma_zone_t zone, void *udata, int flags)
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WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
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"uma_zalloc_arg: zone \"%s\"", zone->uz_name);
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}
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KASSERT(curthread->td_critnest == 0,
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("uma_zalloc_arg: called with spinlock or critical section held"));
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#ifdef DEBUG_MEMGUARD
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if (memguard_cmp_zone(zone)) {
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item = memguard_alloc(zone->uz_size, flags);
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@ -2686,6 +2690,9 @@ uma_zfree_arg(uma_zone_t zone, void *item, void *udata)
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CTR2(KTR_UMA, "uma_zfree_arg thread %x zone %s", curthread,
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zone->uz_name);
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KASSERT(curthread->td_critnest == 0,
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("uma_zfree_arg: called with spinlock or critical section held"));
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/* uma_zfree(..., NULL) does nothing, to match free(9). */
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if (item == NULL)
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return;
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