4.4-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 18e77054de741ef3ed2a2489bc9bf82a318b2d5e ]
Both ashmem_mmap and ashmem_shrink take the ashmem_lock. It may be possible for ashmem_mmap to invoke ashmem_shrink:
-000|mutex_lock(lock = 0x0) -001|ashmem_shrink(?, sc = 0x0) <--- try to take ashmem_mutex again -002|shrink_slab(shrink = 0xDA5F1CC0, nr_pages_scanned = 0, lru_pages -002|= -002|124) -003|try_to_free_pages(zonelist = 0x0, ?, ?, ?) -004|__alloc_pages_nodemask(gfp_mask = 21200, order = 1, zonelist = -004|0xC11D0940, -005|new_slab(s = 0xE4841E80, ?, node = -1) -006|__slab_alloc.isra.43.constprop.50(s = 0xE4841E80, gfpflags = -006|2148925462, ad -007|kmem_cache_alloc(s = 0xE4841E80, gfpflags = 208) -008|shmem_alloc_inode(?) -009|alloc_inode(sb = 0xE480E800) -010|new_inode_pseudo(?) -011|new_inode(?) -012|shmem_get_inode(sb = 0xE480E800, dir = 0x0, ?, dev = 0, flags = -012|187) -013|shmem_file_setup(?, ?, flags = 187) -014|ashmem_mmap(?, vma = 0xC5D64210) <---- Acquire ashmem_mutex -015|mmap_region(file = 0xDF8E2C00, addr = 1772974080, len = 233472, -015|flags = 57, -016|sys_mmap_pgoff(addr = 0, len = 230400, prot = 3, flags = 1, fd = -016|157, pgoff -017|ret_fast_syscall(asm) -->|exception -018|NUR:0x40097508(asm) ---|end of frame
Avoid this deadlock by using mutex_trylock in ashmem_shrink; if the mutex is already held, do not attempt to shrink.
Cc: Greg KH gregkh@linuxfoundation.org Cc: Android Kernel Team kernel-team@android.com Reported-by: Matt Wagantall mattw@codeaurora.org Reported-by: Syed Rameez Mustafa rameezmustafa@codeaurora.org Reported-by: Osvaldo Banuelos osvaldob@codeaurora.org Reported-by: Subbaraman Narayanamurthy subbaram@codeaurora.org Signed-off-by: Laura Abbott lauraa@codeaurora.org [jstultz: Minor commit message tweaks] Signed-off-by: John Stultz john.stultz@linaro.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/staging/android/ashmem.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index e9c74c41aece..b4c425383f99 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -447,7 +447,9 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) if (!(sc->gfp_mask & __GFP_FS)) return SHRINK_STOP;
- mutex_lock(&ashmem_mutex); + if (!mutex_trylock(&ashmem_mutex)) + return -1; + list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { loff_t start = range->pgstart * PAGE_SIZE; loff_t end = (range->pgend + 1) * PAGE_SIZE;