* [PATCH] ext4: Prevent ext4_kvmalloc re-entring the filesystem and deadlocking
@ 2019-12-26 7:10 Naoto Kobayashi
2019-12-26 14:39 ` Theodore Y. Ts'o
0 siblings, 1 reply; 3+ messages in thread
From: Naoto Kobayashi @ 2019-12-26 7:10 UTC (permalink / raw)
To: tytso, adilger.kernel; +Cc: Naoto Kobayashi, linux-ext4
Although __vmalloc() doesn't support GFP_NOFS[1],
ext4_kvmalloc/kvzalloc caller may be under GFP_NOFS context
(e.g. fs/ext4/resize.c::add_new_gdb). In such cases, the memory
reclaim can re-entr the filesystem and potentially deadlock.
To prevent the memory relcaim re-entring the filesystem,
use memalloc_nofs_save/restore that gets __vmalloc() to drop
__GFP_FS flag.
[1] linux-tree/Documentation/core-api/gfp-mask-fs-io.rst
Signed-off-by: Naoto Kobayashi <naoto.kobayashi4c@gmail.com>
---
fs/ext4/super.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 46b6d5b150ac..4a3c9ee63a34 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -43,6 +43,7 @@
#include <linux/uaccess.h>
#include <linux/iversion.h>
#include <linux/unicode.h>
+#include <linux/sched/mm.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
@@ -204,13 +205,32 @@ void ext4_superblock_csum_set(struct super_block *sb)
es->s_checksum = ext4_superblock_csum(sb, es);
}
+static inline void *ext4_vmalloc(size_t size, gfp_t flags, pgprot_t prot)
+{
+ unsigned int nofs_flag = 0;
+ void *ret;
+
+ /**
+ * Although __vmalloc() doesn't support GFP_NOFS, we may be under
+ * GFP_NOFS context here. Hence we need to use memalloc_nofs_save()
+ * to prevent memory reclaim re-entring the filesystem here and
+ * potentially deadlocking.
+ */
+ if (!(flags & __GFP_FS))
+ nofs_flag = memalloc_nofs_save();
+ ret = __vmalloc(size, flags, prot);
+ if (!(flags & __GFP_FS))
+ memalloc_nofs_restore(nofs_flag);
+ return ret;
+}
+
void *ext4_kvmalloc(size_t size, gfp_t flags)
{
void *ret;
ret = kmalloc(size, flags | __GFP_NOWARN);
if (!ret)
- ret = __vmalloc(size, flags, PAGE_KERNEL);
+ ret = ext4_vmalloc(size, flags, PAGE_KERNEL);
return ret;
}
@@ -220,7 +240,7 @@ void *ext4_kvzalloc(size_t size, gfp_t flags)
ret = kzalloc(size, flags | __GFP_NOWARN);
if (!ret)
- ret = __vmalloc(size, flags | __GFP_ZERO, PAGE_KERNEL);
+ ret = ext4_vmalloc(size, flags | __GFP_ZERO, PAGE_KERNEL);
return ret;
}
--
2.16.5
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] ext4: Prevent ext4_kvmalloc re-entring the filesystem and deadlocking
2019-12-26 7:10 [PATCH] ext4: Prevent ext4_kvmalloc re-entring the filesystem and deadlocking Naoto Kobayashi
@ 2019-12-26 14:39 ` Theodore Y. Ts'o
2020-01-08 8:11 ` Naoto Kobayashi
0 siblings, 1 reply; 3+ messages in thread
From: Theodore Y. Ts'o @ 2019-12-26 14:39 UTC (permalink / raw)
To: Naoto Kobayashi; +Cc: adilger.kernel, linux-ext4
On Thu, Dec 26, 2019 at 04:10:08PM +0900, Naoto Kobayashi wrote:
> Although __vmalloc() doesn't support GFP_NOFS[1],
> ext4_kvmalloc/kvzalloc caller may be under GFP_NOFS context
> (e.g. fs/ext4/resize.c::add_new_gdb). In such cases, the memory
> reclaim can re-entr the filesystem and potentially deadlock.
>
> To prevent the memory relcaim re-entring the filesystem,
> use memalloc_nofs_save/restore that gets __vmalloc() to drop
> __GFP_FS flag.
>
> [1] linux-tree/Documentation/core-api/gfp-mask-fs-io.rst
>
> Signed-off-by: Naoto Kobayashi <naoto.kobayashi4c@gmail.com>
Good catch! However, we're not actually using ext4_kvzalloc()
anywhere, at least not any more. And also, all the users of
ext4_kvmalloc() are using GFP_NOFS (otherwise, they would have been
converted over to use the generic kvmalloc() helper function).
So... a cleaner fix would be to (a) delete ext4_kvmazalloc(), (b)
rename ext4_kvmalloc() to ext4_kvmalloc_nofs(), and drop its flags
argument, and then the calls memalloc_nfs_save/restore() to
ext4_kvmalloc_nofs() --- and so we won't need the
if (!(flags & __GFP_FS))
test.
Could you make those changes and resend the patch?
Thanks,
- Ted
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] ext4: Prevent ext4_kvmalloc re-entring the filesystem and deadlocking
2019-12-26 14:39 ` Theodore Y. Ts'o
@ 2020-01-08 8:11 ` Naoto Kobayashi
0 siblings, 0 replies; 3+ messages in thread
From: Naoto Kobayashi @ 2020-01-08 8:11 UTC (permalink / raw)
To: Theodore Y. Ts'o; +Cc: adilger.kernel, linux-ext4
On 2019/12/26 23:39, Theodore Y. Ts'o wrote:
> On Thu, Dec 26, 2019 at 04:10:08PM +0900, Naoto Kobayashi wrote:
>> Although __vmalloc() doesn't support GFP_NOFS[1],
>> ext4_kvmalloc/kvzalloc caller may be under GFP_NOFS context
>> (e.g. fs/ext4/resize.c::add_new_gdb). In such cases, the memory
>> reclaim can re-entr the filesystem and potentially deadlock.
>>
>> To prevent the memory relcaim re-entring the filesystem,
>> use memalloc_nofs_save/restore that gets __vmalloc() to drop
>> __GFP_FS flag.
>>
>> [1] linux-tree/Documentation/core-api/gfp-mask-fs-io.rst
>>
>> Signed-off-by: Naoto Kobayashi <naoto.kobayashi4c@gmail.com>
>
> Good catch! However, we're not actually using ext4_kvzalloc()
> anywhere, at least not any more. And also, all the users of
> ext4_kvmalloc() are using GFP_NOFS (otherwise, they would have been
> converted over to use the generic kvmalloc() helper function).
>
> So... a cleaner fix would be to (a) delete ext4_kvmazalloc(), (b)
> rename ext4_kvmalloc() to ext4_kvmalloc_nofs(), and drop its flags
> argument, and then the calls memalloc_nfs_save/restore() to
> ext4_kvmalloc_nofs() --- and so we won't need the
>
> if (!(flags & __GFP_FS))
>
> test.
>
> Could you make those changes and resend the patch?
>
> Thanks,
>
> - Ted
>
Thank you for the review! I made the changes you suggested and resent
the patch.
[PATCH v2 0/3] ext4: Prevent memory reclaim from re-entering the filesystem and deadlocking
https://marc.info/?l=linux-ext4&m=157743393000807&w=2
Would you review the patch?
Thanks,
- Naoto
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-12-26 7:10 [PATCH] ext4: Prevent ext4_kvmalloc re-entring the filesystem and deadlocking Naoto Kobayashi
2019-12-26 14:39 ` Theodore Y. Ts'o
2020-01-08 8:11 ` Naoto Kobayashi
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