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[PATCH 1/9] staging: ashmem: Avoid deadlock with mmap/shrink

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From: Laura Abbott <lauraa@codeaurora.org>

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>
---
 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 5bb1283..8ae1308 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -441,7 +441,9 @@ 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;
-- 
1.9.1

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[PATCH 0/9] staging: Updates from the Android tree John Stultz <john.stultz@linaro.org> - 2016-01-30 07:10 +0100
  [PATCH 7/9] staging: ion: Handle the memory mapping correctly on x86 John Stultz <john.stultz@linaro.org> - 2016-01-30 07:10 +0100
  [PATCH 2/9] staging: ashmem: Add missing include John Stultz <john.stultz@linaro.org> - 2016-01-30 07:10 +0100
  [PATCH 9/9] staging: ion: Fix page pool cache policy John Stultz <john.stultz@linaro.org> - 2016-01-30 07:10 +0100
  [PATCH 8/9] staging: ion: Add X86 dependency for ION_POOL_CACHE_POLICY John Stultz <john.stultz@linaro.org> - 2016-01-30 07:10 +0100
  [PATCH 1/9] staging: ashmem: Avoid deadlock with mmap/shrink John Stultz <john.stultz@linaro.org> - 2016-01-30 07:10 +0100
  [PATCH 4/9] staging: lowmemorykiller: Make default lowmemorykiller debug message useful John Stultz <john.stultz@linaro.org> - 2016-01-30 07:20 +0100
  [PATCH 5/9] staging: lowmemorykiller: Trace kill events. John Stultz <john.stultz@linaro.org> - 2016-01-30 07:20 +0100
  [PATCH 3/9] staging: lowmemorykiller: Fix task_struct leak John Stultz <john.stultz@linaro.org> - 2016-01-30 07:20 +0100
    Re: [PATCH 3/9] staging: lowmemorykiller: Fix task_struct leak Greg KH <gregkh@linuxfoundation.org> - 2016-02-07 23:50 +0100
      Re: [PATCH 3/9] staging: lowmemorykiller: Fix task_struct leak John Stultz <john.stultz@linaro.org> - 2016-02-08 20:00 +0100
  [PATCH 6/9] staging: ion: Set minimum carveout heap allocation order to PAGE_SHIFT John Stultz <john.stultz@linaro.org> - 2016-01-30 07:20 +0100
    Re: [PATCH 6/9] staging: ion: Set minimum carveout heap allocation  order to PAGE_SHIFT Laura Abbott <labbott@redhat.com> - 2016-02-01 21:30 +0100
  Re: [PATCH 0/9] staging: Updates from the Android tree Laura Abbott <labbott@redhat.com> - 2016-02-01 22:20 +0100
    Re: [PATCH 0/9] staging: Updates from the Android tree John Stultz <john.stultz@linaro.org> - 2016-02-01 22:30 +0100
  Re: [PATCH 0/9] staging: Updates from the Android tree Greg KH <gregkh@linuxfoundation.org> - 2016-02-08 00:00 +0100

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