From 0ea7eeec24be5f04ae80d68f5b1ea3a11f49de2f Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Tue, 17 Oct 2017 16:55:52 +0200 Subject: [PATCH] mm, percpu: add support for __GFP_NOWARN flag Add an option for pcpu_alloc() to support __GFP_NOWARN flag. Currently, we always throw a warning when size or alignment is unsupported (and also dump stack on failed allocation requests). The warning itself is harmless since we return NULL anyway for any failed request, which callers are required to handle anyway. However, it becomes harmful when panic_on_warn is set. The rationale for the WARN() in pcpu_alloc() is that it can be tracked when larger than supported allocation requests are made such that allocations limits can be tweaked if warranted. This makes sense for in-kernel users, however, there are users of pcpu allocator where allocation size is derived from user space requests, e.g. when creating BPF maps. In these cases, the requests should fail gracefully without throwing a splat. The current work-around was to check allocation size against the upper limit of PCPU_MIN_UNIT_SIZE from call-sites for bailing out prior to a call to pcpu_alloc() in order to avoid throwing the WARN(). This is bad in multiple ways since PCPU_MIN_UNIT_SIZE is an implementation detail, and having the checks on call-sites only complicates the code for no good reason. Thus, lets fix it generically by supporting the __GFP_NOWARN flag that users can then use with calling the __alloc_percpu_gfp() helper instead. Signed-off-by: Daniel Borkmann Cc: Tejun Heo Cc: Mark Rutland Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller --- mm/percpu.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/mm/percpu.c b/mm/percpu.c index aa121ce..a0e0c82 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -1329,7 +1329,9 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr) * @gfp: allocation flags * * Allocate percpu area of @size bytes aligned at @align. If @gfp doesn't - * contain %GFP_KERNEL, the allocation is atomic. + * contain %GFP_KERNEL, the allocation is atomic. If @gfp has __GFP_NOWARN + * then no warning will be triggered on invalid or failed allocation + * requests. * * RETURNS: * Percpu pointer to the allocated area on success, NULL on failure. @@ -1337,10 +1339,11 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr) static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, gfp_t gfp) { + bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL; + bool do_warn = !(gfp & __GFP_NOWARN); static int warn_limit = 10; struct pcpu_chunk *chunk; const char *err; - bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL; int slot, off, cpu, ret; unsigned long flags; void __percpu *ptr; @@ -1361,7 +1364,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved, if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE || !is_power_of_2(align))) { - WARN(true, "illegal size (%zu) or align (%zu) for percpu allocation\n", + WARN(do_warn, "illegal size (%zu) or align (%zu) for percpu allocation\n", size, align); return NULL; } @@ -1482,7 +1485,7 @@ fail_unlock: fail: trace_percpu_alloc_percpu_fail(reserved, is_atomic, size, align); - if (!is_atomic && warn_limit) { + if (!is_atomic && do_warn && warn_limit) { pr_warn("allocation failed, size=%zu align=%zu atomic=%d, %s\n", size, align, is_atomic, err); dump_stack(); @@ -1507,7 +1510,9 @@ fail: * * Allocate zero-filled percpu area of @size bytes aligned at @align. If * @gfp doesn't contain %GFP_KERNEL, the allocation doesn't block and can - * be called from any context but is a lot more likely to fail. + * be called from any context but is a lot more likely to fail. If @gfp + * has __GFP_NOWARN then no warning will be triggered on invalid or failed + * allocation requests. * * RETURNS: * Percpu pointer to the allocated area on success, NULL on failure. -- 2.7.4