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libceph: avoid a __vmalloc() deadlock in ceph_kvmalloc() 

The vmalloc allocator doesn't fully respect the specified gfp mask:
while the actual pages are allocated as requested, the page table pages
are always allocated with GFP_KERNEL.  ceph_kvmalloc() may be called
with GFP_NOFS and GFP_NOIO (for ceph and rbd respectively), so this may
result in a deadlock.

There is no real reason for the current PAGE_ALLOC_COSTLY_ORDER logic,
it's just something that seemed sensible at the time (ceph_kvmalloc()
predates kvmalloc()).  kvmalloc() is smarter: in an attempt to reduce
long term fragmentation, it first tries to kmalloc non-disruptively.

Switch to kvmalloc() and set the respective PF_MEMALLOC_* flag using
the scope API to avoid the deadlock.  Note that kvmalloc() needs to be
passed GFP_KERNEL to enable the fallback.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
This commit is contained in:
Ilya Dryomov 2019-08-30 20:44:24 +02:00
parent 6fd4e63483
commit 10c12851a0
1 changed files with 23 additions and 6 deletions
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29
net/ceph/ceph_common.c
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@ -13,6 +13,7 @@
#include <linux/nsproxy.h> #include <linux/nsproxy.h>
#include <linux/parser.h> #include <linux/parser.h>
#include <linux/sched.h> #include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/seq_file.h> #include <linux/seq_file.h>
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/statfs.h> #include <linux/statfs.h>
@ -185,18 +186,34 @@ int ceph_compare_options(struct ceph_options *new_opt,
} }
EXPORT_SYMBOL(ceph_compare_options); EXPORT_SYMBOL(ceph_compare_options);
/*
* kvmalloc() doesn't fall back to the vmalloc allocator unless flags are
* compatible with (a superset of) GFP_KERNEL. This is because while the
* actual pages are allocated with the specified flags, the page table pages
* are always allocated with GFP_KERNEL. map_vm_area() doesn't even take
* flags because GFP_KERNEL is hard-coded in {p4d,pud,pmd,pte}_alloc().
*
* ceph_kvmalloc() may be called with GFP_KERNEL, GFP_NOFS or GFP_NOIO.
*/
void *ceph_kvmalloc(size_t size, gfp_t flags) void *ceph_kvmalloc(size_t size, gfp_t flags)
{ {
if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) { void *p;
void *ptr = kmalloc(size, flags | __GFP_NOWARN);
if (ptr) if ((flags & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS)) {
return ptr; p = kvmalloc(size, flags);
} else if ((flags & (__GFP_IO | __GFP_FS)) == __GFP_IO) {
unsigned int nofs_flag = memalloc_nofs_save();
p = kvmalloc(size, GFP_KERNEL);
memalloc_nofs_restore(nofs_flag);
} else {
unsigned int noio_flag = memalloc_noio_save();
p = kvmalloc(size, GFP_KERNEL);
memalloc_noio_restore(noio_flag);
} }
return __vmalloc(size, flags, PAGE_KERNEL); return p;
} }
static int parse_fsid(const char *str, struct ceph_fsid *fsid) static int parse_fsid(const char *str, struct ceph_fsid *fsid)
{ {
int i = 0; int i = 0;