* + mm-document-__gfp_nofail-must-be-blockable.patch added to mm-unstable branch
@ 2024-07-31 0:39 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2024-07-31 0:39 UTC (permalink / raw)
To: mm-commits, xuanzhuo, vbabka, urezki, torvalds, roman.gushchin,
rientjes, penberg, mst, mhocko, maxime.coquelin, lstoakes, kees,
jasowang, iamjoonsoo.kim, hch, hailong.liu, eperezma, cl,
42.hyeyoo, v-songbaohua, akpm
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 4848 bytes --]
The patch titled
Subject: mm: document __GFP_NOFAIL must be blockable
has been added to the -mm mm-unstable branch. Its filename is
mm-document-__gfp_nofail-must-be-blockable.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-document-__gfp_nofail-must-be-blockable.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Barry Song <v-songbaohua@oppo.com>
Subject: mm: document __GFP_NOFAIL must be blockable
Date: Wed, 31 Jul 2024 12:01:53 +1200
Non-blocking allocation with __GFP_NOFAIL is not supported and may still
result in NULL pointers (if we don't return NULL, we result in busy-loop
within non-sleepable contexts):
static inline struct page *
__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct alloc_context *ac)
{
...
/*
* Make sure that __GFP_NOFAIL request doesn't leak out and make sure
* we always retry
*/
if (gfp_mask & __GFP_NOFAIL) {
/*
* All existing users of the __GFP_NOFAIL are blockable, so warn
* of any new users that actually require GFP_NOWAIT
*/
if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
goto fail;
...
}
...
fail:
warn_alloc(gfp_mask, ac->nodemask,
"page allocation failure: order:%u", order);
got_pg:
return page;
}
Highlight this in the documentation of __GFP_NOFAIL so that non-mm
subsystems can reject any illegal usage of __GFP_NOFAIL with GFP_ATOMIC,
GFP_NOWAIT, etc.
Link: https://lkml.kernel.org/r/20240731000155.109583-3-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Hailong.Liu <hailong.liu@oppo.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/gfp_types.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/include/linux/gfp_types.h~mm-document-__gfp_nofail-must-be-blockable
+++ a/include/linux/gfp_types.h
@@ -215,7 +215,8 @@ enum {
* the caller still has to check for failures) while costly requests try to be
* not disruptive and back off even without invoking the OOM killer.
* The following three modifiers might be used to override some of these
- * implicit rules.
+ * implicit rules. Please note that all of them must be used along with
+ * %__GFP_DIRECT_RECLAIM flag.
*
* %__GFP_NORETRY: The VM implementation will try only very lightweight
* memory direct reclaim to get some memory under memory pressure (thus
@@ -246,6 +247,8 @@ enum {
* cannot handle allocation failures. The allocation could block
* indefinitely but will never return with failure. Testing for
* failure is pointless.
+ * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM.
+ * It should _never_ be used in non-sleepable contexts.
* New users should be evaluated carefully (and the flag should be
* used only when there is no reasonable failure policy) but it is
* definitely preferable to use the flag rather than opencode endless
_
Patches currently in -mm which might be from v-songbaohua@oppo.com are
mm-extend-usage-parameter-so-that-cluster_swap_free_nr-can-be-reused.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios.patch
vpda-try-to-fix-the-potential-crash-due-to-misusing-__gfp_nofail.patch
mm-document-__gfp_nofail-must-be-blockable.patch
mm-bug_on-to-avoid-null-deference-while-__gfp_nofail-fails.patch
mm-prohibit-null-deference-exposed-for-unsupported-non-blockable-__gfp_nofail.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
* + mm-document-__gfp_nofail-must-be-blockable.patch added to mm-unstable branch
@ 2024-08-30 21:45 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2024-08-30 21:45 UTC (permalink / raw)
To: mm-commits, xuanzhuo, xieyongji, vbabka, urezki, torvalds,
roman.gushchin, rientjes, penberg, mst, mhocko, maxime.coquelin,
lorenzo.stoakes, laoar.shao, kees, jasowang, iamjoonsoo.kim, hch,
hch, hailong.liu, eperezma, david, dave, cl, 42.hyeyoo,
v-songbaohua, akpm
[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 5507 bytes --]
The patch titled
Subject: mm: document __GFP_NOFAIL must be blockable
has been added to the -mm mm-unstable branch. Its filename is
mm-document-__gfp_nofail-must-be-blockable.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-document-__gfp_nofail-must-be-blockable.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Barry Song <v-songbaohua@oppo.com>
Subject: mm: document __GFP_NOFAIL must be blockable
Date: Sat, 31 Aug 2024 08:28:22 +1200
Non-blocking allocation with __GFP_NOFAIL is not supported and may still
result in NULL pointers (if we don't return NULL, we result in busy-loop
within non-sleepable contexts):
static inline struct page *
__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct alloc_context *ac)
{
...
/*
* Make sure that __GFP_NOFAIL request doesn't leak out and make sure
* we always retry
*/
if (gfp_mask & __GFP_NOFAIL) {
/*
* All existing users of the __GFP_NOFAIL are blockable, so warn
* of any new users that actually require GFP_NOWAIT
*/
if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
goto fail;
...
}
...
fail:
warn_alloc(gfp_mask, ac->nodemask,
"page allocation failure: order:%u", order);
got_pg:
return page;
}
Highlight this in the documentation of __GFP_NOFAIL so that non-mm
subsystems can reject any illegal usage of __GFP_NOFAIL with GFP_ATOMIC,
GFP_NOWAIT, etc.
Link: https://lkml.kernel.org/r/20240830202823.21478-3-21cnbao@gmail.com
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Hailong.Liu <hailong.liu@oppo.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Xie Yongji <xieyongji@bytedance.com>
Cc: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/gfp_types.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/include/linux/gfp_types.h~mm-document-__gfp_nofail-must-be-blockable
+++ a/include/linux/gfp_types.h
@@ -215,7 +215,8 @@ enum {
* the caller still has to check for failures) while costly requests try to be
* not disruptive and back off even without invoking the OOM killer.
* The following three modifiers might be used to override some of these
- * implicit rules.
+ * implicit rules. Please note that all of them must be used along with
+ * %__GFP_DIRECT_RECLAIM flag.
*
* %__GFP_NORETRY: The VM implementation will try only very lightweight
* memory direct reclaim to get some memory under memory pressure (thus
@@ -246,6 +247,8 @@ enum {
* cannot handle allocation failures. The allocation could block
* indefinitely but will never return with failure. Testing for
* failure is pointless.
+ * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM.
+ * It should _never_ be used in non-sleepable contexts.
* New users should be evaluated carefully (and the flag should be
* used only when there is no reasonable failure policy) but it is
* definitely preferable to use the flag rather than opencode endless
_
Patches currently in -mm which might be from v-songbaohua@oppo.com are
mm-extend-usage-parameter-so-that-cluster_swap_free_nr-can-be-reused.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios.patch
mm-swap-add-nr-argument-in-swapcache_prepare-and-swapcache_clear-to-support-large-folios-fix.patch
mm-rename-instances-of-swap_info_struct-to-meaningful-si.patch
mm-attempt-to-batch-free-swap-entries-for-zap_pte_range.patch
mm-attempt-to-batch-free-swap-entries-for-zap_pte_range-fix.patch
mm-override-mthp-enabled-defaults-at-kernel-cmdline-fix.patch
mm-count-the-number-of-anonymous-thps-per-size.patch
mm-count-the-number-of-partially-mapped-anonymous-thps-per-size.patch
mm-add-nr-argument-in-mem_cgroup_swapin_uncharge_swap-helper-to-support-large-folios.patch
mm-document-__gfp_nofail-must-be-blockable.patch
mm-warn-about-illegal-__gfp_nofail-usage-in-a-more-appropriate-location-and-manner.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
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